Note: "permalinks" may not be as permanent as we would like,
direct links of old sources may well be a few messages off.
> -----Original Message----- > From: drbd-user-bounces at lists.linbit.com > [mailto:drbd-user-bounces at lists.linbit.com] On Behalf Of Lars > Ellenberg > Sent: Tuesday, June 05, 2007 10:55 AM > To: drbd-user at lists.linbit.com > Subject: Re: [DRBD-user] [OT] rsync issues [Was Re: Read performance?] > > On Tue, Jun 05, 2007 at 08:30:12AM -0500, David Masover wrote: > > On Tuesday 05 June 2007 04:12:12 Lars Ellenberg wrote: > > > > > tune the io scheduler(s). > > > get the queue length down. > > > > Ok, which scheduler, and where? I ask because I see tunable > things like: > > > > /sys/block/sda/queue/scheduler > > /sys/block/sda/queue/iosched > > > > But the "queue" directory doesn't even exist for DRBD: > > that is what I'm saying. drbd has no "reqeust queue" in that sense. > (dm-linear has neither, btw., > to draw an analogy between two "virtual" block device drivers...) > drbd just does some housekeeping and then passes the requests along. > > that's why it is very unlikely that it would be drbd's fault > when your reads take too long. > > have a look at your lower level devices. > > generally I recommend deadline. > for your situation (high latency network link) I suggest > small nr_requests. > whether or not that is the real problem, I cannot tell, this has only > been an educated guess. Actually anticipatory might be better here as it will get the read requests down first as the #1 slow-down are write requests. That's my $0.02 > so I also strongly recommend that you do not just tune blindly > something somewhere, because someone (me) told you (based on > *guessing* > where the problem may be) that this *might* have an effetc... > and then it does not help, and you complain that it had no effect... > > first get the facts. > monitor your io subsystem (maybe iostat helps?), > monitor the counters in /proc/drbd, > find out what is really going on. > > until you know what is going on, you cannot really tune. If the link is high-latency I would seriously look into using asynchronous replication in an active-passive setup, then use a network file system with local-cache backing store for sharing the storage... I believe Solaris has NFS caching backing store. I guess that makes $0.04 now... ______________________________________________________________________ This e-mail, and any attachments thereto, is intended only for use by the addressee(s) named herein and may contain legally privileged and/or confidential information. If you are not the intended recipient of this e-mail, you are hereby notified that any dissemination, distribution or copying of this e-mail, and any attachments thereto, is strictly prohibited. If you have received this e-mail in error, please immediately notify the sender and permanently delete the original and any copy or printout thereof.