On 12/12/12 10:09, Andrew Worsley wrote:
On 12 December 2012 01:18, Russell Coker <russell@coker.com.au> wrote:
btrfs subvol snapshot -r /home /home/backup/$(date +%Y-%m-%d:%H:%M)
The above command takes more than 10 seconds on a system with an Intel 120G SSD but less than 1 second on a system with a hard disk identified as "HITACHI HTS72201 DC2Z".
Also I've noticed that every system which uses BTRFS on an Intel 120G SSD gives very poor performance when installing Debian packages (which calls sync()). I'm using the ssd and discard mount options.
Does the Intel SSD just suck for the type of writes that BTRFS does when synchronising things or is there some way of tweaking it for performance?
According to this link fsync is bad on btrfs - perhaps switching to this latest 3.7 kernel might help?
http://www.h-online.com/open/features/What-s-new-in-Linux-3-7-1759862.html Filesystems:
"...A range of optimisations for the still experimental Btrfs are designed to speed up Fsync (File Sync). Applications can now use this command to instruct the kernel to save data that is to be written to the storage devices instead of keeping it in cache. The developers say that these optimisations particularly improve the write performance of virtual machines when the VM images are located on Btrfs filesystems and the guest frequently requests Fsync; Btrfs previously had a reputation for offering rather poor performance in such scenarios....."
That's interesting to know. PostgreSQL always runs like a dog on btrfs, but maybe that was partly to blame.