Mike Meredith

ZFS: Replacing A Functional Mirrored Disk

Computing, Linux, Working Notes No Responses »

Jul 182021

This is a procedure to replace one working drive in a fully functional mirror vdev; if you are replacing a failed disk there is no advantages in following this procedure. Although if you have a somewhat functional disk it may be worth trying.

So why not simply yank out the working disk you want to replace? Well, you can of course and that would work but there is nothing Murphy likes more than a mirrored vdev temporarily down to a single disk – resilvering onto a new disk guarantees a higher chance of failure of the previously working disk (I have actually seen this happening).

So I’m going to describe how to make a three-way mirror with three disks and then detach the disk you wanted to replace.

To do this there are some prerequisites :-

You will need space to install an additional disk into your system; perhaps temporarily in an “unsuitable” location.
You will need a spare SATA controller port to plug the new disk into. If necessary with an additional PCIe SATA controller (which sounds expensive but safety is worth the cost).
You will need a SATA data cable and a SATA power cable.

The first step is to make very careful note of what devices you are going to “swap over” – ideally using their WWNs. If you don’t use WWNs, sorting out which disk is which is going to be a bit trickier.

The second step is to practice the steps involved using a ‘fake’ storage pool backed up by tiny disk files :-

# cd /pool1/temp
# for w in one two three
do
  dd if=/dev/zero of=test-disk-${w}.img bs=1M count=1000
done
# zpool create test mirror /pool1/temp/test-disk-one.img /pool1/temp/test-disk-two.img
# zpool attach test /pool1/temp/test-disk-one.img /pool/temp/test-disk-three.img
# zpool detach test /pool1/temp/test-disk-one.img

That’s pretty much it in a nutshell.

The real process is a bit more disturbing of course and most of the work is physical. The first difference from practice is that when you attach the new disk to one or other of the existing devices within the mirror, you will have to wait until the resilvering process is complete.

Whilst you will receive an estimate for that if you run zpool status, the estimate that you get :-

  scan: resilver in progress since Sun Jul 18 08:20:54 2021
	8.25T scanned at 1.09G/s, 7.28T issued at 981M/s, 8.25T total
	995G resilvered, 88.23% done, 0 days 00:17:16 to go

(Only showing the relevant part as the full output from my system is confusing and deceptive)

Is wildly inaccurate – partially because the resilvering process takes second place to any ordinary file system activity. My own estimate (1 hour per Tbyte) is probably also wildly inaccurate; basically it is done when it is done.

Detaching the old device is fast – you won’t need to sit down to wait for it.

The Resurrected Model F Keyboard

Computing No Responses »

Jun 212021

Available (for now) from www.modelfkeyboards.com.

I do not usually do product reviews, but for various reasons decided to do this – of my newly arrived Model F F77 keyboard. The original IBM keyboard F was produced by IBM between 1981-1994 in various forms, and one keyboard enthusiast decided to re-create one of the more obscure F keyboards because of it’s similarity to modern keyboard layouts and size.

Don’t instantly reject it because it looks old-fashioned – I deliberately went this way and there are plenty of alternative configurations.

Two key points if you decide to buy one :-

Read the manual before starting to fit the key caps. It really will save you time (guess who didn’t?).
If you decide to flash the Via firmware (actually QMK with the Via option turned on), when you run the via program to configure the keyboard, load the relevant json file before wondering why it can’t see your keyboard.

Initial Impressions

Solid. Very solid. And very, very heavy. This keyboard is over 4Kg with a full metal case supposedly of even higher quality than the original.

There are no legs to prop up the back of the keyboard which makes it unusually flat for a normal desktop keyboard. But that is easily solved with something stuffed under the back of the keyboard, and it is sufficiently stable that a prop in the middle of the back doesn’t make it wobbly unless you bang on your keyboard exceptionally hard. And if that happens, just prop it up with two props. Rubber feet are available when you purchase the keyboard.

The layout (bear in mind that I deliberately chose a HHKB-style layout) is pretty much a modern tenkeyless keyboard with various options for the navigation cluster (I have arrows and numbers; other options are available). The raised lip between the alpha cluster and the navigation cluster doesn’t seem to interfere with typing (although your mileage may vary).

The keyboard is supplied with a full set of keycaps, so you can customise the layout to your preferences. They are also exceptionally well printed.

Describing the keyswitch feel is a bit tricky – they are perhaps a bit crisper and lighter than a model M keyswitch, which doesn’t really help if you have never tried one before. The only thing to say is that most keyboard keyswitch connoisseurs will claim that the model F is one of the best keyswitches ever made, and people far more familiar with that keyswitch than I am say that this keyboard matches the original IBM model F keyswitch quality.

In terms of hardware, there is almost nothing to fault with this keyboard; the biggest “fault” is the lack of legs to raise the back of the keyboard. But the original lacked this feature so it is a little unfair.

Firmware

Well this because a bit more nuanced. As originally envisioned, this keyboard would have been equipped with the xwhatis firmware but towards the end of the pre-production process a beta version of QMK was released which supported the keyboard better. My keyboard was delivered with the QMK firmware but without the Via option turned on.

The keyboard with the default firmware works well – there is no real need to swap out the firmware unless you want more advanced features.

But I did.

The first problem I encountered was that the qmk_toolbox gooey is an empty shell under Linux – it doesn’t actually do anything. Which is not widely publicised … and perhaps the distribution of this tool should not make a Linux version so easily available. I ended up using macOS to load the firmware I wanted.

Under Linux it is possible to use dfu-programmer to load the firmware, but as I have not done this myself I can’t comment on how that is done.

And once I managed that, of course I neglected to load the right JSON file into Via so at first it didn’t recognise the keyboard as something that could be controlled. But that was soon put right and I’d programmed the keyboard with the layout I wanted.

Once you have the firmware you want and a suitable way of setting up the firmware layout that you want, the keyboard becomes exceptional. Although the initial configuration is a little rough around the edges, the QMK firmware offers features unbeaten by any commercial keyboard out there – even though Via is not capable of making use of some of them. And frankly, hardware wise, there isn’t a better new keyboard out there.

Is it worth the cost? It is after all expensive but it is actually cheaper than the original IBM model Fs after inflation has been taken into account. And it is the kind of keyboard that could well last a lifetime.

Why Do Research Into The “Bleeding Obvious”?

General No Responses »

Jun 202021

Whenever there’s some research paper on something obvious published in the “popular press” there are always commentators who wonder why. There’s a variety of reason why, but the first is by far the most important.

Just because something is known to be true doesn’t actually make it true. The point of proper research, experimentation, and evaluation is to test the truth of something and to verify that truth. Old wives tales may or may not be true (and some are), but until they are tested they remain just tales.

The second reason is to verify another researcher’s finding – a fact verified by one researcher (or research team) isn’t as fully verified as a fact verified by two or more.

And lastly, researchers have to research to learn their trade. Nobody would trust a plumber who hasn’t yet plumbed or an electrician who hasn’t yet fitted a plug, so why should researchers start with real problems?

Russia: The Chekist State

History, Politics No Responses »

May 092021

I have recently re-read a bunch of stories about the Cold War where the blame for the repressive nature of the Soviet state was placed firmly on the Communist regime. Fair enough you might think, and certainly for most of the 20th century, the former Russian Empire was an extremely repressive regime whilst the Communists were in charge.

Certainly the secret policemen of the Soviets were well known – the GRU, KGB, NKVD, Cheka (where the label “chekist” comes from and all Russian secret police are labelled “chekists”), and others. But the persistent use of Russian secret policemen continues after the collapse of the Communist regime – the GRU is just as strong as they ever were, and there is also the SVR, the FSB, etc. And they’re just as active as ever – including the Salisbury poisonings and similar activities.

What is less well known is that the Russian intelligence services started well before the Communists acquired power in 1917 – the Okhrana. Whilst their headquarters were burned by the revolutionaries, there are persistent left-wing rumours that Okhrana operatives were recruited by the Cheka for their expertise. It is something that is never likely to be proved – these organisations are secret after all, and it did occur over 100 years ago, but the Cheka did become effective surprisingly quickly.

It is easy to blame the communists for their repressive regime, and they certainly deserve plenty of blame but is it really communism that is to blame here? That’s an all too easy assumption to jump on – particularly given the antipathy certain parties (old school European aristocrats and capitalists) have for anything that smacks of depriving them of their ill-gotten gains.

Communism certainly isn’t to blame for the secret police before and after their regime, so wouldn’t it be more accurate to say Russia has a chekist culture that survived two regime changes? Particularly seeing as the current president is a former KGB officer.

Does it matter?

Well for a start, Russia is currently a rogue state using intelligence services in an activist way to kill off critics of their current dictator. And it isn’t communist.

And not all communists are authoritarian communists; they may very well be wrong or misguided but they are not all authoritarians.