> > Lars, > > > > I put MySQL databases on the drbd volume. To back them up, I pause > > them and do LVM snapshots (then rsync the snapshots to an archive > > server). How could I do that with LVM below drbd, since what I want is > > a snapshot of the filesystem where MySQL lives? > > You just snapshot below DRBD, after "quiescen" the mysql db. > > DRBD is transparent, the "garbage" (to the filesystem) of the "trailing drbd > meta data" is of no concern. > You may have to "mount -t ext4" (or xfs or whatever), if your mount and > libblkid decide that this was a "drbd" type and could not be mounted. They are > just trying to help, really. > which is good. but in that case they get it wrong.
Okay, just so I understand.... Suppose I turn md4 into a PV and create one volume group 'vg_under_drbd0', and logical volume 'lv_under_drbd0' that takes 95% of the space, leaving 5% for snapshots. Then I create my ext4 filesystem directly on drbd0. At backup time, I quiesce the MySQL instances and create a snapshot of the drbd disk. I can then mount the drbd snapshot as a filesystem? > > > How severely does putting LVM on top of drbd affect performance? > > It's not the "putting LVM on top of drbd" part. > it's what most people think when doing that: > use a huge single DRBD as PV, and put loads of unrelated LVS inside of that. > > Which then all share the single DRBD "activity log" of the single DRBD volume, > which then becomes a bottleneck for IOPS. > I currently have one big drbd disk with one volume group over it and one logical volume that takes up 95% of the space, leaving 5% of the volume group for snapshots. I run multiple instances of MySQL out of different directories. I don't see a way to avoid the activity log bottleneck problem. _______________________________________________ drbd-user mailing list drbd-user@lists.linbit.com http://lists.linbit.com/mailman/listinfo/drbd-user