On Mon, Nov 15, 2010 at 10:08, Joe Pruett <joey@q7.com> wrote: > >>> BTW, rewriting that 1G file would be normal speed, since >>> the modified chunks have already been copied to the snapshot. >> i'd think that, and you'd think that, but it is not the case. most of >> my tests were done by rewriting the file 4x, and while the snap %used >> (monitored with the 'lvs' command) doesn't keep going up, performance >> stays the same. >> > i did similar tests and i saw that even though i was rewriting the file, > it appeared that the ext3 layer was reallocating new blocks. the > snapshot usage would increase to show 3x the number of blocks i had > thought it should have touched, and then it seemed to stay stable. this > is one of the problems with a block level (as opposed to file level) > snapshot. interestingly, xfs does not show the usage increase as sharply (IIRC--i stopped checking that number after a few runs), but neither is the performance better. _______________________________________________ linux-lvm mailing list linux-lvm@redhat.com https://www.redhat.com/mailman/listinfo/linux-lvm read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/
