On Mon, Nov 15, 2010 at 06:35, Romeo Theriault <romeo.theriault@maine.edu> wrote: > > > On Sat, Nov 13, 2010 at 06:52, chris (fool) mccraw <gently@gmail.com> wrote: >> >> however, snapshots really shoot my system in the foot. in my (12 >> processor, 12GB RAM, x86_64 centos 5.5) server, i have two pricey >> areca hardware raid cards that give me ridiculous write performance: >> i can sustain over 700MByte/sec write speeds (writing a file with dd >> if=/dev/zero bs=1M, twice the size of the raid card's onboard memory >> and timing the write + a sync afterwards) to the volumes on either >> card (both backed by 7 or more fast disks). enabling a single >> snapshot reduces that speed by a factor of 10! enabling more >> snapshots isn't as drastic but still doesn't really scale well: > > > Once you have snapshots and are doing new dd's are you creating new files or > dd'ing over the old file? tried both ways with no obvious performance difference (like i said, sometimes things go up to 30% faster or slower for 1 run, but that's happened doing it both ways). >> no snapshot = ~11sec (727MB/sec) >> 1 snapshot = ~102sec (78MB/sec) >> 2 snapshots = ~144sec (55MB/sec) >> 3 snapshots = ~313sec (25MB/sec) >> 4 snapshots = ~607sec (15MB/sec) > > I would assume a "yes", but does your write performance return to normal > after you remove all the snapshots? absolutely, it does. _______________________________________________ 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/
