Redhatter (VK4MSL)

Jun 022019
 

There’s a couple of truths in life:

  • You don’t get to choose your biological family
  • You don’t get to choose your place of birth

Now, as it happens I ordinarily do not have any real issues with my family or my place of birth, except on one matter: I have never possessed a driver’s license, and really don’t wish to obtain one.

I can get around just fine on my bicycle when I need to. That mode of transport is not nearly as limiting as people think it is. Sure, it’ll take me longer to get places, and I need to perhaps do more planning than most, but I can get where I’m needed.

Yet, time and time again, I run up against the same problem: people assume that people my age, drive cars. People then make the leap to suggest that you’re a useless person if you don’t drive.

I did try to obtain a learner’s permit some time ago. I tried the written test twice: at $20 a pop, at a time when I was unemployed. I wasn’t sure how I was going to fund obtaining a vehicle and paying the necessary fees, but I figured I’d try the first step.

I failed both attempts on one question.

I decided that an identity card was more important: I researched what documentation was required, paid my dues, handed over said documentation, wandered out with a new 18+ card. I figured if I needed to try the driver’s license again, I’d be back.

That was in December 2007. The requirements for obtaining a license have since become more onerous, and let’s face it, there are too many cars on the road today. I’d be looking at taking about 200 hours off from work in order to get the necessary log-book time up and spending tens of thousands of dollars on driving lessons. It isn’t financially worth it.

I re-discovered cycling about 6 months later. I bought a folding bicycle, and started using that to get around, and realised that this was a viable mode of transport for me. Over time, I did longer and longer trips.

The longest I’ve gone unsupported was about 82km. A ride from my home at The Gap to the park at Logan Central takes about 3 hours each way with a couple of rest stops en route. I get going early, take my time, and get there without any trouble.

My work is at Milton, a run of about 10km: I can get there in an hour: faster than public transport. In the early mornings, my times tend to be closer to 45 minutes.

In short, there is just no useful purpose for me to have a car. More to the point, I’d have nowhere to park it. What limited space is available at the front of our property is occupied by a caravan and the neighbours’ numerous cars. If it weren’t for the caravan in fact, it would be all cars belonging to the neighbours.

Moreover, my body actually needs the physical exercise. It’s a fact that moving around is required to keep bodily functions working. You don’t move around enough: bowel movements slow down. I already had one bowel-related health scare this year.

I have not been riding much lately due to scheduling — and I feel my health is suffering greatly because of it.

In spite of this, I still get people, family included, shaking their metaphorical car keys in my face suggesting I should be driving too.

It’s as if, as a non-driver, you’re not welcome in this society. You’re seen as a waste of space — you don’t belong here. We’re seen as “shits” that are there wasting other peoples’ money.

I’ve had a lifetime of that sort of treatment for numerous reasons.

Back in the late 80s, the argument was that I had an Autism diagnosis, therefore I should be going into institutionalised care. Then the same condition was used to argue that I belonged in a special school. At high school, the same reasoning was probably used to put me in the lowest-grade maths and English classes.

I am generally able to focus on a task and do it well. This is probably the reason why I wound up doing double Bachelor-level IT/electronics degrees at uni, and passing both.

I could have instead just been institutionalised. Occupying a tax-payer funded bed. I’d be a record in the NDIS system today. Completely un-employable, generally useless. Definitely not earning >$60000/year doing full-stack software development. There is income tax being paid amongst that — whether my day job is actually worth what I get paid is a debate I’ll leave for others.

The fact remains that I work for a living, and pay my own way.

However, there is a difference to laying out a PCB or writing a code module; and manoeuvring ~600kg of metal travelling at 50+km/hr through suburban roads. One requires focus and patience, the other requires millisecond-level decision-making and reaction times.

I am not someone who thinks well at speed, and I would make no friends driving a car along Waterworks Road at 30km/hr in the morning peak-hour traffic. At 30-40km/hr, I can just manage on the bicycle. I can do up to 60km/hr, but I’m not comfortable at all going that speed!

In a car, you are expected to do the speed limit (50-60km/hr in the case of Waterworks Road). Brisbane’s drivers are not forgiving of anyone who can’t “keep up”.

There are people who have no place driving a car, and I would count myself as being a member of that group. I avoid being on the roads much of the time for that very reason — as a courtesy to drivers who would likely prefer to not be stuck behind a slow cyclist like myself.

Coupled with the health problems: me taking up driving would be an early death sentence. If this is really what is expected, I might as well stop now and get the dying bit over and done with, it’ll be one less person on this planet consuming ever dwindling resources.

It’ll be more humane for me to just quietly go, then to be constantly in and out of medical care for “this” medical condition, or “that” medical condition, costing my employer sick-leave, costing my health fund, occupying resources in our health system, simply because I didn’t get enough exercise.

If a non-driver like me is as useless as people make out, then I guess it won’t hurt anyone that I’m gone. … or maybe we can re-think the “non-drivers are useless” concept. One of the ideas in this paragraph is wrong. I’ve given up trying to decide which!

May 292019
 

It’s been on my TO-DO list now for a long time to wire in some current shunts to monitor the solar input, replace the near useless Powertech solar controller with something better, and put in some more outlets.

Saturday, I finally got around to doing exactly that. I meant to also add a low-voltage disconnect to the rig … I’ve got the parts for this but haven’t yet built or tested it — I’d like to wait until I have done both,but I needed the power capacity. So I’m running a risk without the over-discharge protection, but I think I’ll take that gamble for now.

Right now:

  • The Powertech MP-3735 is permanently out, the Redarc BCDC-1225 is back in.
  • I have nearly a dozen spare 12V outlet points now.
  • There are current shunts on:
    • Raw solar input (50A)
    • Solar controller output (50A)
    • Battery (100A)
    • Load (100A)
  • The Meanwell HEP-600C-12 is mounted to the back of the server rack, freeing space from the top.
  • The janky spade lugs and undersized cable connecting the HEP-600C-12 to the battery has been replaced with a more substantial cable.

This is what it looks like now around the back:

Rear of the rack, after re-wiring

What difference has this made? I’ll let the graphs speak. This was the battery voltage this time last week:

Battery voltage for 2019-05-22

… and this was today…

Battery voltage 2019-05-29

Chalk-and-bloody-cheese! The weather has been quite consistent, and the solar output has greatly improved just replacing the controller. The panels actually got a bit overenthusiastic and overshot the 14.6V maximum… but not by much thankfully. I think once I get some more nodes on, it’ll come down a bit.

I’ve gone from about 8 hours off-grid to nearly 12! Expanding the battery capacity is an option, and could see the cluster possibly run overnight.

I need to get the two new nodes onto battery power (the two new NUCs) and the Netgear switch. Actually I’m waiting on a rack-mount kit for the Netgear as I have misplaced the one it came with, failing that I’ll hack one up out of aluminium angle — it doesn’t look hard!

A new motherboard is coming for the downed node, that will bring me back up to two compute nodes (one with 16 cores), and I have new 2TB HDDs to replace the aging 1TB drives. Once that’s done I’ll have:

  • 24 CPU cores and 64GB RAM in compute nodes
  • 28 CPU cores and 112GB RAM in storage nodes
  • 10TB of raw disk storage

I’ll have to pull my finger out on the power monitoring, there’s all the shunts in place now so I have no excuse but to make up those INA-219 boards and get everything going.

May 252019
 

So recently I was musing about how I might go about expanding the storage on the cluster. This was largely driven by the fact that I was about 80% full, and thus needed to increase capacity somehow.

I also was noting that the 5400RPM HDDs (HGST HTS541010A9E680), now with a bit of load, were starting to show signs of not keeping up. The cases I have can take two 2.5″ SATA HDDs, one spot is occupied by a boot drive (120GB SSD) and the other a HDD.

A few weeks ago, I had a node fail. That really did send the cluster into a spin, since due to space constraints, things weren’t as “redundant” as I would have liked, and with one disk down, I/O throughput which was already rivalling Microsoft Azure levels of slow, really took a bad downward turn.

I hastily bought two NUCs, which I’m working towards deploying… with those I also bought two 120GB M.2 SSDs (for boot drives) and two 2TB HDDs (WD Blues).

It was at that point I noticed that some of the working drives were giving off the odd read error which was throwing Ceph off, causing “inconsistent” placement groups. At that point, I decided I’d actually deploy one of the new drives (the old drive was connected to another node so I had nothing to lose), and I’ll probably deploy the other shortly. The WD Blue 2TB drives are also 5400RPM, but unlike the 1TB Hitachis I was using before, have 128MB of cache vs just 8MB.

That should boost the read performance just a little bit. We’ll see how they go. I figured this isn’t mutually exclusive to the plans of external storage upgrades, I can still buy and mod external enclosures like I planned, but perhaps with a bit more breathing room, the immediate need has passed.

I’ve since ordered another 3 of these drives, two will replace the existing 1TB drives, and a third will go back in the NUC I stole a 2TB drive from.

Thinking about the problem more, one big issue is that I don’t have room inside the case for 3 2.5″ HDDs, and the motherboards I have do not feature mSATA or M.2 SATA. I might cram a PCIe SSD in, but those are pricey.

The 120GB SSD is only there as a boot drive. If I could move that off to some other medium, I could possibly move to a bigger SSD in place of the 120GB SSD, maybe a ~500GB unit. These are reasonably priced. The issue is then where to put the OS.

An unattractive option is to shove a USB stick in and boot off that. There’s no internal USB ports, but there are two front USB ports in the case I could rig up to an internal header so they’re not sticking out like a sore thumb(-drive) begging to be broken off by a side-wards slap. The flash memory in these is usually the cheapest variety, so maybe if I went this route, I’d buy two: one for the root FS, the other for swap/logs.

The other option is a Disk-on-Module. The motherboards provide the necessary DC power connector for running these things, and there’s a chance I could cram one in there. They’re pricey, but not as bad as going NVMe SSDs, and there’s a greater chance of success squeezing this in.

Right now I’ve just bought a replacement motherboard and some RAM for it… this time the 16-core model, and it takes full-size DIMMs. It’ll go back in as a compute node with 32GB RAM (I can take it all the way to 256GB if I want to). Coupled with that and a purchase of some HDDs, I think I’ll let the bank account cool off before I go splurging more. 🙂

May 242019
 

Recently, I had a failure in the cluster, namely one of my nodes deciding to go the way of the dodo. I think I’ve mostly recovered everything from that episode.

I bought some new nodes which I can theoretically deploy as spare nodes, Core i5 Intel NUCs, and for now I’ve temporarily decommissioned one of my compute nodes (lithium) to re-purpose its motherboard to get the downed storage node back on-line. Whilst I was there, I went and put a new 2TB HDD in… and of course I left the 32GB RAM in, so it’s pretty much maxxed out.

I’d like to actually make use of these two new nodes, however I am out of switch capacity, with all 26 ports of the Linksys LGS-326AU occupied or otherwise reserved. I did buy a Netgear GS748T with the intention of moving across to it, but never got around to doing so.

The principle matter here being that the Netgear requires a wee bit more power. AC power ratings are 100-250V, 1.5A max. Now, presumably the 1.5A applies at the 100V scale, that’s ~150W. Some research suggested that internally, they run 12V, that corresponds to about 8.5A maximum current.

This is a bit beyond the capabilities of the MIC29712s.

I wound up buying a DC-DC power supply, an isolated one as that’s all I could get: the Meanwell SD-100A-12. This theoretically can take 9-18V in, and put out 12V at up to 8.5A. Perfect.

Due to lack of time, it sat there. Last week-end though, I realised I’d probably need to consider putting this thing to use. I started by popping open the cover and having a squiz inside. (Who needs warranties?)

The innards of the GS-748Tv5, ruler for scale

I identified the power connections. A probe around with the multimeter revealed that, like the Linksys, it too had paralleled conductors. There were no markings on the PSU module, but un-plugging it from the mainboard and hooking up the multimeter whilst powering it up confirmed it was a 12V output, and verified the polarity. The colour scheme was more sane: Red/Yellow were positive, Black/Blue were negative.

I made a note of the pin-out inside the case.

There’s further DC-DC converters on-board near the connector, what their input range is I have no idea. The connector on the mainboard intrigued me though… I had seen that sort of connector before on ATX power supplies.

The power supply connector, close up.

At the other end of the cable was a simple 4-pole “KK”-like connector with a wider pin spacing (I think ~3mm). Clearly designed with power capacity in mind. I figured I had three options:

  1. Find a mating connector for the mainboard socket.
  2. Find a mating header for the PSU connector.
  3. Ram wires into the plug and hot-glue in place.

As it happens, option (1) turned out easier than I thought it would be. When I first bought the parts for the cluster, the PicoPSU modules came with two cables: one had the standard SATA and Molex power connectors for powering disk drives, the other came out to a 4-pin connector not unlike the 6-pole version being used in the switch.

Now you’ll note of those 6 poles, only 4 are actually populated. I still had the 4-pole connectors, so I went digging, and found them this evening.

One of my 4-pole 12V connectors, with the target in the background.

As it happens, the connectors do fit un-modified, into the wrong 4 holes — if used unmodified, they would only make contact with 2 of the 4 pins. To make it fit, I had to do a slight modification, putting a small chamfer on one of the pins with a sharp knife.

After a slight modification, the connector fits where it is needed.

The wire gauge is close to that used by the original cable, and the colour coding is perfect… black corresponds to 0V, yellow to +12V. I snipped off the JST-style connector at the other end.

I thought about pulling out the original PSU, but then realised that there was a small hole meant for a Kensington-style lock which I wasn’t using. No sharp edges, perfect for feeding the DC cables through. I left the original PSU in-situ, and just unplugged its DC output.

The DC input leads snake through the hole that Netgear helpfully provided.

Bringing the DC power input to the outside.

Before putting the screws in, I decided to give this a test on the bench supply. The switch current fluctuates a bit when booting, but it seems to settle on about 1.75A or so. Not bad.

Testing the switch running on 12V

Terminating this, I decided to use XT-60 connectors. I wanted something other than the 30A “powerpoles” and their larger 50A cousins that are dotted throughout the cluster, as this needed to be regulated 12V. I did not want to get it mixed up with the raw 12V feed from the batteries.

I ran some heavier gauge cable to the DC-DC PSU, terminated with the mating XT-60 connector and hooked that up to my PSU. Providing it with 12V, I dialled the output to 12V exactly. I then gave it a no-load test: it held the output voltage pretty good.

Next, I hooked the switch up to the new PSU. It fired up and I measured the voltage now under load: it still remained at 12V. I wound the voltage down to 9V, then up to 15V… the voltage output never shifted. At 9V, the current consumption jumps up to about 3.5A, as one would expect.

Otherwise, it seemed to be content to draw under 2A so the efficiency of the DC-DC converter is pretty good.

I’ll need to wire in a new fuse box to power everything, but likely the plan will be to decommission the 16-port 100Mbps switch I use for the management network, slide the 48-port switch in its place, then gradually migrate everything across to the new switch.

Overall, the modding of this model switch was even less invasive than that of the Linksys. It’s 100% reversible. I dare say having posted this, there’ll be a GS748Tv6 that’ll move the 240V PSU to the mainboard, but for now at least, this is definitely a switch worth looking at if 12V operation is needed.

May 242019
 

So, in my workplace we’re developing a small energy/water metering device, which runs on a 6LoWPAN network and runs OpenThread-based firmware. The device itself is largely platform-agnostic, requiring a simple CoAP gateway to provide it with a configuration blob and history write end-point. The gateway service I’m running is intended to talk to WideSky.

One thorny issue we need to solve before deploying these things in the wild, is over-the-air updates. So we need a way to transfer the firmware image to the device over the mesh network. Obviously, this firmware image needs to be digitally signed and hashed using a strong cryptographic hash — I’ve taken care of this already. My problem is downloading an image that will be up to 512kB in size.

Thankfully, the IETF has thought of this, the solution to big(gish) files over CoAP is Block-wise transfers (RFC-7959). This specification gives you the ability to break up a large payload into smaller chunks that are powers of two in size between 16 and 2048 bytes.

6LoWPAN itself though has a limitation: the IEEE 802.15.4 radio specification it is built on cannot send frames bigger than 128 bytes. Thus, any message sent via this network must be that size or smaller. IPv6 has a minimum MTU of 1280 bytes, so how do they manage? They fragment the IPv6 datagram into multiple 802.15.4 frames. The end device re-assembles the fragments as it receives them.

The catch is, if a fragment is lost, you lose the entire datagram, there’s no repeats of individual fragments, the entire datagram must be re-sent. The question in my mind was this: Is it faster to rely on block-wise transfers to break the payload up and make lots of small requests, or is it faster to rely on 6LoWPAN fragmentation?

The test network here has a few parts:

  • The target device, which will be downloading a 512kB firmware image to a separate SPI flash chip.
  • The border router, which provides a secure IPv6 tunnel to a cloud host.
  • The cloud server which runs the CoAP service we’ll be talking to.

The latency between the office (in Brisbane) and the cloud server (in Sydney) isn’t bad, about 30~50ms. The CoAP service is built using node-coap and coap-polka.

My CoAP requests have some overheads:

  • The path being downloaded is about 19 bytes long.
  • There’s an authentication token given as a query string, so this adds an additional 12 bytes.

The data link is not 100% reliable, with the device itself dropping some messages. This is leading to some retransmits. The packet loss is not terrible, but probably in the region of around 5%. Over this slightly lossy link, I timed the download of my 512kB firmware image by my device with varying block size settings.

Note that node-coap seems to report a “Bad Option” error for szx=0 and szx=7, even though both are legitimately within specification. (I’d expect node-coap to pass szx=7 through and allow the application to clamp it to 6, but it seems node-coap‘s behaviour is to report “Bad option”, but then pass the payload through anyway.)

Size Exponent (szx)Block sizeStart time (UTC)End time (UTC)Effective data rate
6102403:27:0403:37:52809B/s
551203:41:2503:53:40713B/s
425603:57:1504:16:16458B/s
312804:17:4604:54:17239B/s
26404:56:0905:54:53150B/s
13223:31:3301:39:4468B/s

It remains to be seen how much multiple hops and outdoor atmospherics affect the situation. A factor here is how quickly the device can turn-around between processing a response and sending the next request, which in this case is governed by the speed of the SPI flash and its driver.

Effects on “busy” networks

So, I haven’t actually done any hard measurements here, but doing testing on a busier network with about 30 nodes, the block size equation tips more in favour of a smaller block size.

I’ll try to quantify the delays at some point, but right now 256 byte blocks are the clear winner, with 512 and 1024 byte block transfers proving highly unreliable. The speed advantage between 1k and 512 bytes in ideal conditions was a big over 10%… which really doesn’t count for much. At 256 bytes, the speed difference was about 43%, quite significant. You’re better off using 512-byte blocks if the network is quiet.

On a busy network, with all the retransmissions, smaller is better. No hard numbers yet, but right now at 256 byte blocks, the effective rate is around 118 bytes/sec. I’ll have to analyse the logs a bit to see where 512/1024 byte block sizes sat, but the fact they rarely completed says it all IMO.

Slow and steady beats fast and flakey!

May 182019
 

Seriously, if you think this is a good way to earn some yuan, think again. I just got this email this afternoon:


Dear CEO,
(It’s very urgent, please transfer this email to your CEO. If this email affects you, we are very sorry, please ignore this email. Thanks)
We are a Network Service Company which is the domain name registration center in China.
We received an application from Hua Hai Ltd on May 14
, 2019. They want to register ” stuartl.longlandclan ” as their Internet Keyword and ” stuartl.longlandclan .cn “、” stuartl.longlandclan .com.cn ” 、” stuartl.longlandclan .net.cn “、” stuartl.longlandclan .org.cn ” 、” stuartl.longlandclan .asia “、domain names, they are in China and Asia domain names. But after checking it, we find ” stuartl.longlandclan ” conflicts with your company. In order to deal with this matter better, so we send you email and confirm whether this company is your distributor or business partner in China or not?
 


Best Regards
**************************************
Mike Zhang | Service Manager
Cn YG Domain (Head Office)
Contact details censored as I do not wish to promote their business
*************************************

The wording is identical to that seen in this article on squelchdesign. Knowing this to be a scam, I did two things:

  1. As per my standard policy, I forwarded it to SpamCop. The source of the email was Baidu’s own network.
  2. I figured since it’s obviously a scam and since these people seemingly do not learn from the skirmishes with others, I’d have some fun with them:

On 18/5/19 11:46 am, Mike Zhang wrote:

Dear CEO, (It’s very urgent, please transfer this email to your CEO. If this email affects you, we are very sorry, please ignore this email. Thanks)

You want this to go to my CEO? Does every individual person in China have their own personal CEO? Is that why they have such a big population? Please keep in mind what the .id.au domain suffix is for: INDIVIDUALS.

We are a Network Service Company which is the domain name registration center in China.

Ahh, so you must know the rules around domain registrations, like the .id.au domain suffix being non-commercial.

We received an application from Hua Hai Ltd on May 14, 2019. They want to register ” stuartl.longlandclan ” as their Internet Keyword and ” stuartl.longlandclan .cn “、” stuartl.longlandclan .com.cn ” 、” stuartl.longlandclan .net.cn “、” stuartl.longlandclan .org.cn ” 、” stuartl.longlandclan .asia “、domain names, they are in China and Asia domain names.

They must be rich. They also wanted bellavitosi .cn, bellavitosi.com.cn, bellavitosi.net.cn, bellavitosi.org.cn, bellavitosi.asia, formula1-dictionary.cn, formula1-dictionary.com.cn, formula1-dictionary.net.cn, formula1-dictionary.org.cn and formula1-dictionary.asia.

What does this group do? Are they a subsiduary of BaoYuan Ltd? I hear pan xiaohong has wealth that rivals Jack Ma.

But after checking it, we find ” stuartl.longlandclan ” conflicts with your company. In order to deal with this matter better, so we send you email and confirm whether this company is your distributor or business partner in China or not?

Well, this “company” does not exist, so can’t possibly have a partner in China. I say to them, go ahead and register those domain names, I dare you, it’ll cost you a lot more than it will cost me.

Errm, yeah… the SEO spammers are slowly learning not to mess with me as I’ll just report the email as spam and will tweak mail server settings to ensure you stay blocked. Or I may choose to publicly ridicule you like I have done here.

The worst they can do is actually follow through and register all those domains, which will cost them an absolute bloody fortune (.asia domains are not cheap!) and my content is already well known with the search engines — it’s not like I rely on my online presence for an income anyway as I have a day job. Anything I do here is for self-education and training.

All this mob is doing, is destroying the image of some innocent company in Hong Kong, which are likely nothing to do with this scam. Seriously guys, get a real job!

May 142019
 

Well, it had to happen some day, but I was hoping it’d be a few more years off… I’ve had the first node failure on the cluster.

One of my storage nodes decided to keel over this morning, some time between 5 and 8AM… sending the cluster into utter chaos. I tried power cycling the host a few times before finally yanking it from the DIN rail and trying it on the bench supply. After about 10 minutes of pulling SO-DIMMs and general mucking around trying to coax it to POST, I pulled the HDD out, put that in an external dock and connected that to one of the other storage nodes. After all, it was approaching 9AM and I needed to get to work!

A quick bit of work with ceph-bluestore-tool and I had the OSD mounted and running again. The cluster is moaning that it’s lost a monitor daemon… but it’s still got the other two so provided that I can keep O’Toole away (Murphy has already visited), I should be fine for now.

This evening I took a closer look, tried the RAM I had in different slots, even with the RAM removed, there’s no signs of life out of the host itself: I should get beep codes with no RAM installed. I ran my multimeter across the various power rails I could get at: the 5V and 12V rails look fine. The IPMI BMC works, but that’s about as much as I get. I guess once the board is replaced, I might take a closer look at that BMC, see how hackable it is.

I’ve bought a couple of spare nodes which will probably find themselves pressed into monitor node duty, two Intel NUC7I5BNHs have been ordered, and I’ll pick these up later in the week. Basically one is to temporarily replace the downed node until such time as I can procure a more suitable motherboard, and the other is a spare.

I have a M.2 SATA SSD I can drop in along with some DDR4 RAM I bought by mistake, and of course the HDD for that node is sitting in the dock. The NUCs are perfectly fine running between 10.8V right up to 19V — verified on a NUC6CAYS, so no 12V regulator is needed.

The only down-side with these units is the single Ethernet port, however I think this will be fine for monitor node duty, and two additional nodes should mean the storage cluster becomes more resilient.

The likely long-term plan may be an upgrade of one of the compute nodes. For ~$1600, I can get a A2SDi-16C-HLN4F, which sports 16 cores and takes full-size DDR4 DIMMs. I can then rotate the board out of that into the downed node.

The full-size DIMMS are much more readily available in ECC format, so that should make long-term support of this cluster much easier as the supplies of the SO-DIMMs are quickly drying up.

This probably means I should pull my finger out and actually do some of the maintenance I had been planning but put off… largely due to a lack of time. It’s just typical that everything has to happen when you are least free to deal with it.

Apr 112019
 

Lately, I had a need for a library that would talk to a KISS TNC and allow me to exchange UI frames over an AX.25 network.

This is part of a project being undertaken by Brisbane Area WICEN Group. We’ve been tasked with the job of reporting scans from RFID tag readers back to base… and naturally we’ll be using the AX.25 network we’re already familiar with. The plan is to use APRS messaging (to keep things simple) to submit the location, time and hardware address of each RFID read.

For this, I needed something I also need for this project, a tool to encode and decode the UI frames. I had initially thought of just using LinBPQ or similar to provide the interface to AX.25, but in the end, it was easier for me to write my own simple AX.25 stack from scratch.

aioax25 obviously is nowhere near a replacement for other AX.25 stacks in that it only encodes and decodes frames, but it’s a first step in that journey. This library is written for Python 3.4 and up using the asyncio module and pyserial. At the moment I have used it to somewhat crudely send and receive APRS messages, and so with a bit of work, it’ll suffice for the WICEN project.

That does mean I’m not shackled in terms of what bits I can set in my AX.25 headers. One limitation I have with my mapping of 6LoWHAM addresses to AX.25 addresses is that I cannot represent all characters or the “group” bit.

This lead to the limitation that if I defined a group called VK4BWI-0, that group may not have a participant with the call-sign of VK4BWI-0 because I would not be able to differentiate group messages from direct messages.

By writing my own AX.25 stack, I potentially can side-step that limitation: I can utilise the reserved bits in a call-sign/SSID to represent this information. I avoided their use before because the interfaces I planned on using did not expose them, but doing it myself means they’re directly accessible. The AX.25 protocol documentation states:

The bits marked “r” are reserved bits. They may be used in an agreed-upon manner in individual networks. When not implemented, they should be set to one.

https://www.tapr.org/pub_ax25.html

Now, the question is, if I set one to 0, would it reach the far end as a 0? If so, this could be a stand-in for the group bit — stored inverted so that a 1 represents a unicast destination and 0 represents a group.

The other option is to just prepend the left-over bits to the start of the message payload. This has the bonus that I can encode the full-callsign even if that call-sign does not fit in a standard AX.25 message.

So a message sent to VK4FACE-6 (let’s pretend F-calls can use packet for the sake of an example) would be sent to AX.25 SSID VK4FAC-6, and the first few bytes would encode the missing E and the group/unicast bit. If the station VK4FAC were also on frequency, the software stack at their end would need to filter based on those initial payload bytes.

We support 8-character call-signs, so we need to represent 2 left-over characters plus a group bit. Add space for two-more characters for the source call-sign (which may not be a group), we require about 3 bytes.

At this point we might as well use 4, store the extra bytes as 7-bit ASCII, with the spare MSBs of each byte encoding the group bit and one spare bit. An extra 8 bits is bugger all really even at 1200 baud.

Obviously, NET/ROM has no knowledge of this. Stations that are on the other side of a non-6LoWHAM digipeater need to explicitly source-route their hops to reach the rest of a mesh network, and the nodes the other side need to “remember” this source route.

This latter scheme also won’t work for connected mode, as there’s no scope to shoehorn those bytes in the information field and still remain AX.25 compatible — it will only work for 6LoWHAM UI frames.

Anyway, it’s food for thought.

Apr 032019
 

I got this pair of text messages today…

Before I answer, I have 3 questions of my own:

  1. Why are you calling me “BILL”?  Pretty sure that is not printed anywhere on my birth certificate.
  2. Who on earth is “Claire” that I allegedly had a “service experience” with.  (I do hope that isn’t a euphemism!)
  3. The phone number this was sent to is a Telstra service: first activated in 2001.  0439 is a Telstra prefix.  Why the F### ask me?

I do have a SIM card that is an Optus pre-paid, that’s installed in the Kite, along-side a Telstra pre-paid.  I haven’t turned that phone on in a good month or so (I should fire it up just to keep the battery fresh though).

I’d never install that Optus phone in this phone however: pretty sure the phone I received this SMS on is locked to Telstra so it wouldn’t get a service if I tried.

Given you can’t get my name right, and you clearly haven’t checked your records properly, let me finish with this: Why would I recommend you?

Feb 152019
 

One problem I face with the cluster as it stands now is that 2.5″ HDDs are actually quite restrictive in terms of size options.

Right now the whole shebang runs on 1TB 5400RPM Hitachi laptop drives, which so far has been fine, but now that I’ve put my old server on as a VM, that’s chewed up a big chunk of space. I can survive a single drive crash, but not two.

I can buy 2TB HDDs, WD make some and Scorptec sell them. Seagate make some bigger capacity drives, however I have a policy of not buying Seagate.

At work we built a Ceph cluster on 3TB SV35 HDDs… 6 of them to be exact. Within 9 months, the drives started failing one-by-one. At first it was just the odd drive being intermittent, then the problem got worse. They all got RMAed, all 6 of them. Since we obviously needed drives to store data on until the RMAed drives returned, we bought identically sized consumer 5400RPM Hitachi drives. Those same drives are running happily in the same cluster today, some 3 years later.

We also had one SV35 in a 3.5″ external enclosure that formed my workplace’s “disaster recovery” back-up drive. The idea being that if the place was in great peril and it was safe enough to do so, someone could just yank this drive from the rack and run. (If we didn’t, we also had truly off-site back-up NAS boxes.) That wound up failing as well before its time was due. That got replaced with one of the RMAed disks and used until the 3TB no longer sufficed.

Anyway, enough of that diversion, long story short, I don’t trust Seagate disks for 24/7 operation. I don’t see other manufacturers (other than Seagate e.g. WD, Samsung, Hitachi) making >2TB HDDs in the 2.5″ form factor. They all seem to be going SSD.

I have a Samsung 850EVO 2TB in the laptop I’m writing this on, bought a couple of years ago now, and so far, it has been reliable. The cluster also uses 120GB 850EVOs as OS drives. There’s now a 4TB version as well.

The performance would be wonderful and they’d reduce the power consumption of the cluster, however, 3 4TB SSDs would cost $2700. That’s a big investment!

The other option is to bolt on a 3.5″ HDD somehow. A DIN-rail mounted case would be ideal for this. 3.5″ high-capacity drives are much more common, and is using technology which is proven reliable and is comparatively inexpensive.

In addition, by going to bigger external drives it also means I can potentially swap out those 2.5″ HDDs for SSDs at a later date. A WD Purple (5400RPM) 4TB sells for $166. I have one of these in my desktop at work, and so far its performance there has been fine. $3 more and I can get one of the WD Red (7200RPM) 4TB drives which are intended for NAS use. $265 buys a 6TB Toshiba 7200RPM HDD. In short, I have options.

Now, mounting the drives in the rack is a problem. I could just make a shelf to sit the drive enclosures on, or I could buy a second rack and move the servers into that which would free up room for a second DIN rail for the HDDs to mount to. It’d be neat to DIN-rail mount the enclosures beside each Ceph node, but right now, there’s no room to do that.

I’d also either need to modify or scratch-make a HDD enclosure that can be DIN-rail mounted.

There’s then the thorny issue of interfacing. There are two options at my disposal: eSATA and USB3. (Thunderbolt and Firewire aren’t supported on these systems and adding a PCIe card would be tricky.)

The Supermicro motherboards I’m using have 6 SATA ports. If you’re prepared to live with reduced cable lengths, you can use a passive SATA to eSATA adaptor bracket — and this works just fine for my use case since the drives will be quite close. I will have to power down a node and cut a hole in the case to mount the bracket, but this is doable.

I haven’t tried this out yet, but I should be able to use the same type of adaptor inside the enclosure to connect the eSATA cable to the HDD. Trade-off will be further reduced cable distances, but again, they don’t need to go more than 30cm, it’ll most likely work fine.

The other interface option is USB 3.0. The motherboards have two back-panel USB 3.0 connectors and inside, two USB 3.0 ports I can potentially expose. This can be hot-plugged without changing my cluster as it stands now. The down-side is that USB incurs a greater CPU overhead than SATA.

During my migration to BlueStore, I used exactly this to provide a “temporary” OSD disk… a 1TB 7200RPM WD black in a HDD dock. The performance of that was fine, and in that case, I was willing to put up with the overhead as it was temporary.

External eSATA cases seem to be going the way of the dodo, I haven’t seen many available for sale from my usual suppliers. USB 3.0 seems to have taken over, probably because for most uses, it is “good enough”. I did ask about whether one is preferred over the other for Ceph OSD use on the Ceph mailing list, but heard nothing.

As it was, prior to undertaking the migration, I bought such a case, an el’cheapo Simplecom SE-325, along with a 4TB WD Blue for the actual drive. I was tossing up between that, and a LaCiE “Porsche” 4TB drive, but the winning factor of this was that I’d know what I was buying — the LaCiE drive could have had anything in there, manufacturers can and sometimes do substitute components in different manufacturing runs, buying the case and drive separately didn’t run that risk.

The case and drive did the job. I hooked the drive up to my laptop (I had forgotten xhci_hcd support in the storage nodes’ kernels, which I have since fixed) and pulled a snapshot of every VM disk (Rados block device) off the Ceph cluster onto this drive as a raw disk image so I would not lose data. The drive easily kept up with the GbE link I had to the downstairs switch, and a core in the Core i5-3320M in this laptop is probably on par with the ones in the Avoton C2750s running the show.

To DIN-rail mount this, I’d need to make a cradle to take the case, and I’d need to hack some forced-ventilation into the top cover, which isn’t a difficult job. (Drill some holes, then use a nibbler tool to cut slots, then mount a small fan.)

The original PSU for this case is a 12V 2A wall wart, easily substituted with a 12V 3A LDO such as the LM1085IT-12. I may even be able to squeeze it and a heatsink into the case. I presently use one of these with the border router with a small heatsink, and so far, no problems.

If I later want eSATA, I can unscrew the original PCB and should be able to hack that in.

Short term, I can place a temporary shelf atop the battery cases and sit the HDDs there until I figure out more permanent arrangements.

Right now I’ve been battling a few health problems (sharp-eyed readers may recognise the box of “gunk” in the background which is now empty and the accompanying documentation — I’ll know more next Friday morning), and so I’ll wait until I know the outcome of those tests as there’s no point in building something grand if I’m not going to be around to enjoy it.