Note: "permalinks" may not be as permanent as we would like,
direct links of old sources may well be a few messages off.
J.B., Are you making use of LVM snapshots by any chance? I've read reports of extremely awful performance as a result of LVM2 CoW code -- whether you're on the trunk volume or any snapshot volumes: http://www.nikhef.nl/~dennisvd/lvmcrap.html 1GB took 20sec to write w/o snapshots, 16min with snapshots! If you're using LVM snapshots on that host, then perhaps that explains the performance penalties you've noticed. On 09/10/10 06:47, trekker.dk at abclinuxu.cz wrote: > Hello, > > I'm trying to use DRBD as storage for virtualised guests. DRBD is > created on top of LVM partition, all LVM partitions reside on single > software RAID1 array (2 disks) > > In this setup the DRBD is supposed to operate in standalone mode most > of the time, network connections will only come into play when > migrating a guest to another host (That's why I can't use RAID - DRBD > - LVM - there can be more than 2 hosts and guests need to be able to > migrate anywhere.) > > So I did very simple benchmark, created an LVM partition and tried to > write into it and then read the data: > > # dd if=/dev/zero of=/dev/mapper/obrazy2-pokus \ > bs=$((1024**2)) count=16384 > # dd if=/dev/mapper/obrazy2-pokus of=/dev/null \ > bs=$((1024**2)) count=16384 > > Both tests yielded about 80MB/s throughput. > > Then I created a DRBD on top of that LVM and retried the test: > > # /sbin/drbdmeta 248 v08 /dev/mapper/obrazy2-pokus internal create-md > # drbdsetup 0 disk \ > /dev/mapper/obrazy2-pokus /dev/mapper/obrazy2-pokus \ > internal --set-defaults --create-device > # drbdsetup 0 primary -o > > Reading performace was the same, but writes dropped to about 35MB/s, > with flushes disabled (drbdsetup ... -a -i -D -m) about 45MB/s. > > I'd understand that, if the device was connected over network, but in > standalone mode I was expecting DRBD to have roughly the same > performance as underlying storage. > > My question: is that drop in write throughput normal or could there be > some error in my setup, which is causing it? > > System setup is: Debian, kernel 2.6.34 from kernel.org, drbd-utils > 8.3.7. Also tested on kernel 2.6.35.4 from kernel.org. > > Regards, > J.B. > _______________________________________________ > drbd-user mailing list > drbd-user at lists.linbit.com > http://lists.linbit.com/mailman/listinfo/drbd-user -- Joshua West Senior Systems Engineer Brandeis University http://www.brandeis.edu