Date: Thu, 17 Apr 2008 12:18:43 +0100 From: Pete French <petefrench@ticketswitch.com> To: stable@freebsd.org Subject: Dreadful gmirror performance, though each half works fine Message-ID: <E1JmS8Z-000BPO-9x@dilbert.ticketswitch.com>
next in thread | raw e-mail | index | archive | help
I am trying to run a system with a pair of drives mirrored under gmirror, one of thhem being local and the other remote using ggated. I've measured the performance of both the local and the remote drive individually, and they are both fine - can get about 70meg/second out of them. I've also created mirrors with oone drive in of each of thhem, and these perform fine too - i.e. each mirror with one drive still gives me around 65-70 meg/second. When I create a mirror by taking one of them and adding the other the mirror resyncs at full speed (i.e. I see network traffic of around 70 meg/second and the time taken to complete the resync correspnds to that rate). ...and then the performance of the drive drops to a few k/second ?! I am running myself on top of the mirror drives, but it runs like treacle. During this time there is no intensive CPU activity, no intensive network activits and no intensive disc activity - the machine just seems completely cuiqre. but doing an 'ls' on the mirror drive takes forever. If i then take a drive out using 'gmirror deactivate' the command freezes up for a couple of minutes, but enevtiually comes back. I then do a 'gmirror status' and that also takes a minute or so to come back. During the time these commands are running I get 100% disc activity in 'gstat' on the drive I took out - though almost no actual data being trasferred. ...at this point I am back to the situation I started with (a mirror with only one disc in it) but the performance is still horrible. I can stop the mirror, detach the ggate drive, reattach, restart - still horrible performance, even though I have now gone back to the situation I had before. Has anyone else seen this ? I've tried various configurations, accross several machines, all with the same result. It looks like ggate gets itself into a state where it is suddenly very slow, and then cannot recover from that. This doesnt happen with local gmirrors, nor if I replace the underlying ggate with iscsi (though that causes kernel panics but that's another story). Any advice ? -pete. PS: All machines are amd64/7.0-RELEASE
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?E1JmS8Z-000BPO-9x>