On Tue, Apr 10, 2012 at 11:31:20AM +1000, Toby Corkindale wrote:
On 05/04/12 17:42, Craig Sanders wrote:
i'm wondering if iscsi kind of obsoletes drbd, and if mdadm raid1 over two iscsi exports would be better than drbd.
Oooh, no, don't do that. We've tried it. It didn't work out.
It sounds like a good idea at first, but every time you need to reboot one or other of the iscsi targets (eg. for kernel updates or suchlike) you'll need to rebuild the RAID array, and the performance of that over ethernet blows.
does using a bitmap help? with local disks, it makes a massive improvement to resync times.
part of my curiosity is due to the fact that i prefer zfs to lvm, and iscsi ... when i get time i intend to experiment with ganeti and see if i can come up with a zfs+iscsi+mdadm storage module for it as an alternative to lvm+drbd.
I'd be interested to hear your experiences of that, if you get it up and running.
well, given that i'll be experimenting with it on virtual machines, i'm not expecting the performance to be anything to write home about. i'm more interested in finding out how viable it is, and what the behaviour is when bad things happen. and whether it works better than lvm+drbd. another option would be for two ganeti nodes to create a zvol each, export them via iscsi, build a mirrored zpool from them, and give that to the VM...i suspect that would work much better than mdadm over iscsi. craig -- craig sanders <cas@taz.net.au>