testing HS/SR - 1 vs 2 performance
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From: Greg Smith on 7 May 2010 08:04 Erik Rijkers wrote: > Everything together: the raid is what Areca call 'raid10(1E)'. > (to be honest I don't remember what that 1E exactly means - > extra flexibility in the number of disks, I think). > Standard RAID10 only supports an even number of disks. The 1E variants also allow putting an odd number in. If you're using an even number, like in your case, the results are the same until you start losing drives, at which point the degradation performance pattern changes a bit due to differences in how things are striped. See these for more info: http://bytepile.com/raid_class.php and http://en.wikipedia.org/wiki/Non-standard_RAID_levels#IBM_ServeRAID_1E http://publib.boulder.ibm.com/infocenter/eserver/v1r2/index.jsp?topic=/diricinfo/fqy0_craid1e.html I don't think using RAID1E has anything to do with your results, but it is possible given your test configuration that part of the difference you're seeing relates to where on disk blocks are stored. If you take a hard drive and write two copies of something onto it, the second copy will be a little slower than the first. That's just because how drive speed drops over the surface as you move further along it. There's some examples of what that looks like at http://projects.2ndquadrant.it/sites/default/files/pg-hw-bench-2010.pdf on pages 21-23. Returning to your higher level results, one of the variables you weren't sure how to account for was caching effects on the standby--the possibility that it just didn't have the data cached the same as the master impacting results. The usual way I look for that is by graphing the pgbench TPS over time. In that situation, you can see it shoot upwards over time, very obvious pattern. Example at http://projects.2ndquadrant.it/sites/default/files/pgbench-intro.pdf on pages 36,37. -- Greg Smith 2ndQuadrant US Baltimore, MD PostgreSQL Training, Services and Support greg(a)2ndQuadrant.com www.2ndQuadrant.us -- Sent via pgsql-hackers mailing list (pgsql-hackers(a)postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers |