btrfs: why I don’t see it as “rampant layer violation”

There are many who aren’t thrilled with the btrfs design, seeing it as a “rampant layer violation.”  What does this mean, and why do I think that’s not a problem?

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Garmin 610 again

I previously blogged on my Garmin 610.  Another bug bear came up last weekend.  Although it’s not well publicized, the 610 has a biking mode.  I went for a bike ride.  And the lap button is positioned such that when you’re biking, the angle of your wrist results in it getting pushed by accident.  So I did 3 laps.  It’s not the end of the world, and definitely better it be the lap button than the stop button.  But it’s not ideal.


I agree with The Australian on this one.  We have increased spending on education very substantially over the last few years.  It hasn’t turned into results. The Gonsky review wasn’t directly about increasing spending, it was about how we allocate spending.  The problem is that reallocating funding implies some get more and some get less.  That is politically unpalatable, so Julia committed that no school would be worse off.  That resulted in needing to increase funding by $6.5B p.a. to fully implement Gonski.

Increasing spending again won’t improve results any more than it did in the past.  What is needed is a focus on how we improve teaching.  Reducing class sizes has a small improvement, but it’s not the best spend of money.  Improving teacher quality is a much better path, but involves taking on the unions.  Julia won’t do that.  A Liberal government might, but better still would for this to go back to being a state responsibility, and the Federal government just get out of it.  Across Australia we could then see different results in different places, and the States could innovate.  Better still would be to push down to individual school level, with bulk funding and allowance of vouchers so that parents can send children to private schools more easily.  No chance of that happening any time soon.

What is Gillard up to?

In the past week we’ve had lots of announcements.  It seems to boil down to:

  • More money in education – in theory $6.5B per annum, in reality $10B over 4 years, with only $1B in the first year
  • More money in disabilities – the NDIS will cost many billions per annum (nobody seems to know quite how many)
  • More money in health – filling a gap that the federal government created by revisiting the population growth numbers and reducing funding to states
  • A funding hole in the mining tax and the carbon tax
  • A plan to cut concessions on superannuation

The numbers don’t add up.  I can’t help but think that this is all about taking care of the base without being serious about having to implement any of these changes – it’s a plan for saving the furniture without any risk of having to actually be in government.

Virtual machine backup size

As noted in an earlier post, I’ve created a process to backup my virtual machines.

The trick is that much of the disk space I allocated for my virtual machines is empty – they’re running about 25% full.  So ideally my backup would be 25% or less of the total machine size, particularly after I zip the extracted file.

As noted in that previous post, I’m just backing up the image itself directly.  If the bits of the file system that aren’t used were all filled with zeroes, it would zip really well.  In reality, the bits of a file system that aren’t used are filled with whatever was there before – essentially random stuff.  That compresses much less well.

So, my aim is to zero fill the spare space.  This comes in two flavours:

1. The swap space, which is within the drbd device

2. The ext4 file system.

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BTRFS RAID6 coming

I’ve been keeping an eye on btrfs for some time, it provides a next generation file system for Linux that is in many ways equivalent to ZFS on Solaris.  It’s still relatively new, so not something you’d trust irreplaceable data to, but long term it will provide some compelling features:

  • Checksumming of all data and metadata.  As drives get larger the law of averages / large numbers says that some pieces of data will become corrupt.  For media files this isn’t critical, you might get a pixel different on one frame of a movie.  For a spreadsheet or a program it could be critical.  Checksumming will tell you if your data is wrong on disk
  • Integrated RAID support.  RAID 0 and 1 are built-in, and it allows different RAID levels on different directories, and different for metadata v’s data.  RAID5/6 has been “coming” for some time, but not available yet
  • Because the RAID is integrated, and because of checksumming, where a discrepancy is identified between two drives btrfs can pick the correct one to repair from – not only does it make your data redundant, it can sensibly fix it when something goes wrong (md RAID basically randomly picks one block so as to get back in synch)

The RAID5/6 patches have gone up into an experimental tree, which means they’re on the way to the kernel proper, I’d guess maybe 3.10.  Which is huge news.  Refer:

Newspaper headlines: Gillard in trouble, Greens split

Interesting headlines today.  The Australian has “Shorten urged to end paralysis” above the fold, smaller story about the split with the Greens.  They have their eye on the ball, not the man.  The other papers seem to be focusing on the “news” that the Greens and Labor will put some distance between themselves before the election.  It certainly tells us a bit about the editorial line of the different rags….

The pressure is definitely building on Julia again, but I think she’ll ride this one out.  There’ll be a small (within margin of error) improvement in the polls, that will stay people’s hand.  April is the time to do it if it’s happening at all.