Category Archives: Computers

Miscellanious Computing

That’s not a moon, that’s the IPv6 address range!

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IPv6 is big. You just won’t believe how vastly, hugely, mind- bogglingly big it is. I mean, you may think it’s a long way down the subnet to the IPv4 broadcast address, but that’s just peanuts to IPv6. – not quite DA

Whether or not you think IPv6 is a good thing the sheer size of the addressable range is very very easy to underestimate, so Aaron Toponce’s method of translating it into a (rather large) image is a rather nice one. I love his final little comment:

(If I wanted to fit the entire IPv6 space on my physical monitor right now, each pixel would need to represent 192,903,836,122,980,988,357,922,113,056,557 IP addresses. Cool.)

🙂

Off to NZ for a week!

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Having successfully recovered from all the RAID pain we’ve gone through recently at work (lesson: do not trust HW RAID and have good backups – which we did) I’m off to New Zealand for a week with Donna courtesy of my time off in lieu – sweet as! 😉

When I’m back I’ll write up what happened with the RAID, honest..

Grub in Lenny won’t boot when the kernel is on disk 26 or more

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Will hopefully get to report this tomorrow to the Grub folks and the Debian maintainer, but basically it looks like the grub in Lenny can’t cope with systems with lots of disks. We have two storage systems that we use software RAID on and seem to have hit a few problems with grub.

  1. grub-mkdevicelist only iterates over the first 16 SCSI drives, so if your boot partition is beyond /dev/sdp then you’ll get an error about it not being able to find the boot partition. This is hard coded into a loop in grub-mkdevicelist.c so you can tweak that up to 25 disks safely.
  2. if you have more than 25 drives (as we do on one system) you’ll hit the next problem as your devices start getting called /dev/sdaa, /dev/sdab, etc.. grub-mkdevicelist doesn’t handle that correctly. If you bump the number in that loop beyond 25 as it will start trying to find /dev/sd{ , /dev/sd| , etc, which it then rejects as they don’t exist. Again that’s fairly easy to work around with a conditional check in get_scsi_disk_name() to at least cope with the sd?? pattern (Reported as bug #514967). This then leads to the last problem of..
  3. Even having the correct device map when your boot device is on /dev/sdab1 still results in Grub in Lenny not being able to locate the boot partition, and we’ve not had time to chase that down any further (reported as bug #514976).

Comments of the type “serve you right for having too many disks” will be ignored.. 😉

More cores, less speed

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An interesting set of simulations at Sandia of multi-core systems have been reported:

A team of researchers simulated key algorithms for deriving knowledge from large data sets. The simulations show a significant increase in speed going from two to four multicores, but an insignificant increase from four to eight multicores. Exceeding eight multicores causes a decrease in speed. Sixteen multicores perform barely as well as two, and after that, a steep decline is registered as more cores are added.

The reason for this is fairly well known, but it’s nice to see numbers put to the effect..

The problem is the lack of memory bandwidth as well as contention between processors over the memory bus available to each processor.

The original Sandia press release has more information.

Taxing Questions for Liechtenstein

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I was listening to the BBC From Our Own Correspondent Podcast which had a great piece by John Sweeney about murky going ons in Liechtenstein. Part of it made me think that they’ve been going to the same school as Microsoft:

The next morning we heard that there was a banking seminar at the university on openness. This being Liechtenstein, the openness meeting was closed, at least to us.

John also has a wicked sense of humour..

Imagine my disappointment on discovering that Liechtenstein was, in fact, the most boring place on earth. I’m used to boredom – I work for the BBC, for heaven’s sake – but Liechtenstein was as dull as ditchwater, no duller. They bank behind closed doors. They create fuzzy trusts behind close doors. They make false teeth. And then they go to bed. The person who most looked like a ruthless killer was Howard, and he was the BBC producer.

Well worth a listen.. 😉

ENOKOGAN – Kogan Agora is dead (for now)

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Oh well, so much for the dream, this was on the Kogan blog this afternoon:

I’m disappointed to have to tell you that the Kogan Agora has to be delayed indefinitely. This delay comes due to potential future interoperability issues.

Sounds like this was partly due to wanting to keep the device compatible with future Android versions needing better screens:

One of the potential issues is the screen size and resolution. It seems developers will be creating applications that are a higher resolution than the Agora is currently capable of handling. […] In order to fully appreciate the feature-rich applications Android developers will be creating in coming months and years, the Agora must be redesigned.

I hope that whatever they come up with still has a real keyboard..

btrfs for 2.6.29

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This news from Chris Mason on the linux-btrfs mailing list:

Hello everyone,

Just a quick note that Linus merged the btrfs unstable repository into the mainline kernel. I’ll cut a new stable release of btrfs-progs on Monday to go with it (for now the unstable repo is the best choice).

I’d like to thank everyone who contributed to the code, tested, reviewed, documented, helped organize and otherwise helped Btrfs get as far as it has. It wouldn’t have been possible without you.

There is a lot of work to do before we can really declare Btrfs finished, but this is a huge step forward.

Yay! Congratulations Chris.. 🙂

For those who want to know more about btrfs, please check out its wiki page..