On 06/20/2012 02:34 PM, Phil Frost wrote:
What OS and kernel version are you running? Also, when you say slower with both nodes present, is it slower enough to indicate that fsync is working?
They're old CentOS boxes running 2.6.18. So far as the latency, I'm not sure, but I doubt it's responsible; we have a direct 10G link between the two machines. For what it's worth, we are running XFS, so it's not a very good comparison. I don't use EXT4 in production environments.
In the case of small synchronous writes, I'd expect any difference in latency to be indistinguishable from measurement error.
FusionIO drives here. Our PostgreSQL sync calls, based on checkpoint logging, are almost 2x slower with a connected DRBD resource, than when it's in standalone. About what you'd expect, actually.
We have a test cluster on a simple RAID0 with much newer OS running a 3.2 kernel, too. That's where I noticed a Pacemaker failover would attempt to start the LVM service before DRBD was done promoting during a manual failover. I had to add a 2-second start delay, which tells me the DRBD RA is not waiting long enough before returning control to Pacemaker. I suppose that could be sync related, but I haven't run any specific tests.
For that matter, is anyone absolutely sure that fsync is working on their DRBD devices?
I can confirm it works in our existing setup. We run a 10ktps OLTP database on Postgres and have experienced a few unplanned outages where we failed over to the other node. If DRBD was having trouble, we'd have ripped it out and bought a SAN long ago.
I haven't done enough tests in our dev environment with the updated kernel/DRBD to know for sure. If I have time later, I'll run a quick dd test.
-- Shaun Thomas OptionsHouse | 141 W. Jackson Blvd. | Suite 500 | Chicago IL, 60604 312-444-8534 stho...@optionshouse.com ______________________________________________ See http://www.peak6.com/email_disclaimer/ for terms and conditions related to this email _______________________________________________ drbd-user mailing list drbd-user@lists.linbit.com http://lists.linbit.com/mailman/listinfo/drbd-user
