On Fri, Feb 04, 2005 at 10:26:36AM +0000, Nigel Jewell wrote: > Dear Ben, Oh yeah, or you could take a look at http://www.drbd.org/ -Ben > Thank you for your detailed reply. It is always refreshing to get a > decent response on a mailing list ;) . > > >Sure. You see the -c in you export line. Don't put it there. That puts > >the device in (the very poorly named) uncached mode. This does two > >things. > >One: It causes the server to use direct IO to write to the exported > >device, > >so your read performance will take a hit. Two: It will time out after > >a period (default to 10 sec). After gnbd times out, it must be able > >to fence > >the server before it will let the requests fail. This is so that you > >know > >that the server isn't simply stalled and might write out the requests > >later > >(if gnbd failed out, and the requests were rerouted to the backend > >storage over > >another gnbd server, if the first server wrote it's requests out > >later, it > >could cause data corruption). > > > > > > My understanding was that the "-c" put the device in cached mode, as > described here: > > http://www.redhat.com/docs/manuals/csgfs/admin-guide/s1-gnbd-commands.html > > Or are you saying that by not putting the "-c" put its in uncached mode? > > >This means that to run in uncached mode, you need to have a cluster > >manager and > >fencing devices, which I'm not certain that you have. > > > > > > No we don't as we didn't really see the need, given what we want to do. > > >I've got some questions about your setup. Will this be part of a > >clustered > >filesystem setup? If it will, I see some problems with your mirror. When > >other nodes (including the gnbd server node A) write to the exported > >device, > >these writes will not appear on the local partion of B. So won't your > >mirror > >get out of sync? If only B will write to the exported device, (and > >that's > >the only way I see this working) you can probably get by with nbd, which > >simply fails out if it loses connection. > > > > > > The intention of the setup was to have two hosts both exporting an > unmounted device, and the alternative device using it as a RAID-1 > device. Then to use heartbeat to mount and unmount the partitions as > required. For example: > > HOST A: > > /dev/hda1 (md0, ext3, mounted) > /dev/hda2 (ext3, unmounted, gnbd_exported as A) > /dev/gnbd/B (md0, ext3, mounted) > > HOST B: > > /dev/hda1 (ext3, unmounted, gnbd_exported as B) > /dev/hda2 (md0, ext3, mounted) > /dev/gnbd/A (md0, ext3, mounted) > > I hope that makes sense. > > If so, does what we are trying to achieve sound sensible? Any > gotchas/advice? > > -- > Nige. > > PixExcel Limited > URL: http://www.pixexcel.co.uk > > -- > > Linux-cluster@xxxxxxxxxx > http://www.redhat.com/mailman/listinfo/linux-cluster
