8 Jul
2013
8 Jul
'13
14:31
On 7/8/13 10:17 AM, David Disseldorp wrote:
On Mon, 8 Jul 2013 14:14:19 +0200 David Sterba <dsterba@suse.cz> wrote:
VM and database loads do not play well with the COW mechanism. The NOCOW file attribute (chattr +C) fixed the performance problems with VM images for me and reportedly for others. This comes at a price, the checksums are turned off for the file.
IIUC, that also removes the ability to instantaneously clone VM images using cp --reflink. I'd consider that a pretty severe cost for a workload where Btrfs normally excels.
Yep, though it might be possible to CoW when the extent is shared and write-in-place when it's not. -Jeff -- Jeff Mahoney SUSE Labs