All posts by Huw Lynes

Badass

My descent into responsible adulthood continues apace. The vacuum cleaner that came with my current flat appears to be powered by elastic bands. It doesn’t suck. So finally in a fit of practicality and technophillia I bought one of these.

To quote one of Neal Stephenson’s characters:

“Until a man is twenty-five, he still thinks, every so often, that under the right circumstances he could be the baddest motherfucker in the world. If I moved to a martial-arts monastery in China and studied real hard for ten years. If my family was wiped out by Columbian drug dealers and I swore myself to revenge. If I got a fatal disease, had one year to live, devoted it to wiping out street crime. If I just dropped out and devoted myself to being bad.”

At 30 the fact that I’m excited about a new vacuum cleaner proves that this is no longer, if it ever was, true for me.

On the plus side. My new vacuum cleaner totally rocks.

Kernel Humour

The unfortunate limerick cascade on the Linux Kernel Mailing List is a horror to behold.

However I have to share with you Alan Cox’s song about memory management to the tune of the Beatles Eleanor Rigby.

Ah look at all the laundered pages
Ah look at all the laundered pages

Handling Pages
Pick up the list and the link where kswap has been
A paging scheme
Runs down the I/O
Watching the queues that now keep me a list of the store
Who is it for

All the laundered pages
Where do they all come from
All the laundered pages
Where do they all belong

Meeting bdflush
Writing the pages of a disk file that no one will clear
No task comes near
Look at it working
Sleeping a lot in the night when there’s no pressure there
What does it care

All the laundered pages
Where do they all come from
All the laundered pages
Where do they all belong

Ah look at all the laundered pages
Ah look at all the laundered pages

Oracle DB
Died under load and was freed along with its name
No admin came
Good old bdflush
Wiping the dirt from the pages as it walks down the chain
Nothing was aged

All the laundered pages
(Ah look at all the laundered pages)
Where do they all come from
All the laundered pages
(Ah look at all the laundered pages)
Where do they all belong

Moving ZFS filesystems between pools

When I originally set up the ZFS on my development v880 I added the internal disks as a raidz together with two volumes off the external fibre-channel array. As is the way with these things the development box has gradually become a production box. And I now realise that if the server goes pop I can’t just move the fibre-channel to another server because the ZFS pool contains that set of internal scsi disks.

To my horror I now discover that you can’t remove a top-level device (vdev in ZFS parlance) from a pool. Fortunately I have two spare volumes on the array so I can create a new pool and transfer the existing zfs filesystems to it. Here is a quick recipe for transferring zfs filesystems whilst keeping downtime to a minimum.

zfs snapshot oldpool/myfilesystem@snapshot1

zfs send oldpool/myfilesystem@snapshot1 | zfs receive newpool/myfilesystem

this will take a while but the filesystem can stay in use while you are doing it. Once this finishes you need to shut down any services that are relying on the filesystem and unmount it.

zfs unmount oldpool/myfilesystem

And take a new snapshot.

zfs snapshot oldpool/myfilesystem@snapshot2

you can now do an incremental send of the difference between the two snapshots which should be very quick.

zfs send -i oldpool/myfilesystem@snapshot1 \
             oldpool/myfilesystem@snapshot2 | zfs receive newpool/myfilesystem

Now you can point the services at the new filesystem and start over until all the filesystems on the original pool have been transferred.

I Hate Network Rail

I’m supposed to be going on a site-visit to Birmingham University today. Instead I will be in the office because none of the trains I need are running.
Apparently rain is now an adverse weather condition.

edit 26/06/2007
OK given that thousands of people have been evacuated from their homes, maybe it does count as adverse weather.

Inner Life of a Cell

Very cool video from Harvard, taking us on a whistle-stop tour of the inside of a cell. The first version is the condensed version with all the pretty animation and no actual science.

There is also the full 8 minute version where generic-science-guy actually explains what’s going on.

Free as in Freedom, Bitch

Most people will no doubt have already seen this delightful interview with Bill Hilf. In this interview Bill, who I had previously taken to be an energetic and eloquant linux engineer working on Windows/Linux integration issues, reveals himself to be not so much the Devil, as the man who goes and gets the Devil a pack of cigarettes. In my more charitable moment I imagine Bill dragged around south-east asia by a brutal MSFT minder, forced to say things he doesn’t really believe: “It spreads the FUD or it gets the hose again.”

“The Free Software movement is dead. Linux doesn’t exist in 2007. Even Linus has got a job today.”

OK Bill, I’m surprised no-one has told you this, but when people say Free software they mean it was released under a Free Software license. It doesn’t mean that the person that wrote it wasn’t paid.

“most customers run a distribution – RedHat, Novell, Suse or Mandriva. Most of the work on maintaining the Linux kernel is done by developers working for these distributions”

Indeed most people don’t build a linux distribution from scratch bootstrapping everything from the compiler on up themselves. In other news: if you stand outside in the rain you’ll get wet. Jonothon Corbet’s recent study for LWN shows that Bill is indeed correct that most kernel code comes from paid developers. But, and I hate to keep banging this drum, that doesn’t mean it isn’t Free Software. This just shows that real companies with real business models can write free software without the world coming to an end. This stands in stark contrast to what some people think.

“Hilf accused his former employers, IBM, of starting a standards war simply because they wanted a part of the Office market. People do not want ODF (Open Document Format), but they want a way to control the information they create, he claimed.”

ODF has been open since Star/OpenOffice was open-sourced in 2000. In order to make it as easy as possible for people to write their own implementation of ODF the time was taken to properly standardise it. This process involved at least IBM and Sun, and happened before OpenXML was even talked about. I can’t even begin to grasp how this could be characterised as a standards war.

There is more in a similar vein, but I’m going to choose to assume that Bill contracted cerebral malaria while he was in Thailand.