RE: storage service times
Date: Thu, 3 Jan 2008 14:30:28 -0500
The rule-of-thumb we used to use at EMC was that DBAs started to notice and complain about storage performance at around a 10-15ms service time. On lightly loaded arrays, it wasn't uncommon to see 1-3ms service times, and on arrays that were doing some work the numbers you are seeing were right in line.
Now, of course, "performance" is dependent on "results" - so if the database isn't providing the performance you need, then maybe the array isn't keeping up. But as an abstract value, 4-7ms service times don't offend me.
[mailto:oracle-l-bounce_at_freelists.org] On Behalf Of Dan Norris Sent: Thursday, January 03, 2008 12:51 PM To: Oracle L
Subject: storage service times
I'm looking over a system that has what I believe to be a much-larger-than-average service time for read and write I/O.
Hitachi (branded Sun 9990) storage array via 2xFC HBAs 8x 12 Gb storage array LUNs striped 256k stripe width using VxVM on the host = about 90Gb volumes
Given that (somewhat incomplete) footprint, what are your first "knee-jerk" reactions to these times for a 1-hour statspack report interval:
Av Av Av Av Buffer Av Buf Reads Reads/s Rd(ms) Blks/Rd Writes Writes/s WaitsWt(ms)
-------------- ------- ------ ------- ------------ -------- ----------
397,958 111 8.3 1.0 79,676 22 4,114 4.8
410,619 114 9.2 1.0 8,695 2 161,789 7.1
159,094 44 8.3 1.0 137,040 38 31 5.2
These are rolled up to the tablespace level and I'm particularly interested in comparing with other people's Av Rd(ms) (the 3rd col) and Av Wt(ms) (the last col). I'll go first...my gut feeling, based on past experiences elsewhere, is that 6+ ms seems about 50-100% higher than I expected to see.
I know I'm getting service times from Oracle without offering any info on what the OS or Vol Mgr say about the service times viewed from those points of view, but the service time in the DB is the only metric that matters at this point. I'll dig in to the other layers as necessary when I start debugging. I'm looking for your opinion to see if this is a problem or if I just set my expectations too high. :-)