Re: [gentoo-user] Fast file system for cache directory with lot's of files

[Alecks Gates <alecks.g@gmail.com>]

On Tue, Aug 14, 2012 at 12:50 PM, Michael Hampicke <gentoo-user@hadt.biz> wrote:
> Am 14.08.2012 19:42, schrieb Volker Armin Hemmann:
>> Am Dienstag, 14. August 2012, 13:21:35 schrieb Jason Weisberger:
>>> Sure, but wouldn't compression make write operations slower?  And isn't he
>>> looking for performance?
>>
>> not really. As long as the CPU can compress faster than the disk can write
>> stuff.
>>
>> More interessting: is btrfs trying to be smart - only compressing compressible
>> stuff?
>>
>
> It does do that, but letting btrfs check if the files are already
> compressed, if you know, that they are compressed, is a waste of cpu
> cycles :)
>

Also look into the difference between compress and compress-force[0].
I wonder how much overhead checking whether or not to compress a file
costs.  I use mount options similar to Helmut and get great results:
defaults,autodefrag,space_cache,compress=lzo,subvol=@,relatime

But most of my data is compressible.  Compression makes such a huge
difference, it surprises me.  Apparently on this Ubuntu system it
automatically makes use of all files on / as a subvolume in "@".
Interesting.

Anyway, btrfs-progs does include basic fsck now but I wouldn't use it
for anything serious[1].


[0] https://btrfs.wiki.kernel.org/index.php/Mount_options
[1] https://btrfs.wiki.kernel.org/index.php/Btrfsck