On 07/30/2011 04:02 AM, Raphael Hertzog wrote:
On Fri, 29 Jul 2011, Nicolas STRANSKY wrote:
Simplistic tests involving "tar" show that the disk is able to produce
throughputs that are about 30x higher than the ones I observe when dpkg
is unpacking files (60MB/s vs. 2MB/s). I have tried a couple
workarounds but they didn't change anything: using dpkg with
--force-unsafe-io or mounting / with nodatacow.
Did you try running your apt-get under eatmydata? If it solves your issue
it means the slowness is the result of the fsync() that dpkg is doing.
And I heard it multiple times that btrfs was not very efficient when you
are doing lots of fsync() but I am afraid there's not much we can do to
improve this if we want to keep the reliabily of dpkg in general.
I didn't know before about eatmydata but it indeed completely solves my
issue! dist-upgrades are like a hundred times faster. So I guess the
problem is really that the multiple fsync() in dpkg won't work
efficiently with btrfs, which is a shame! It makes it almost impossible
to use btrfs on / with Debian.
Thanks,
Nicolas
--
Nico
GPG FBFA4781
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