SUMMARY: D1000 performances issues with solstice

Thanks to Karl Vogel, Rami Aubourg, Kevin Buterbaugh for their responses

Original Post:

I have D1000 connected to my SUN box (SCSI) with solstice volumes running 
oracle applications. I have been noticing sluggish response from the disks. 
Top shows close to 70% iowait.
iostat reveals all the meta devices show above 50 ms service time at appr. 
20% busy. As per adrian cockcroft's performance tips, any thing above 30 ms 
service_t with 5% or above busy should be considered a bottleneck. Can any 
one of you guide me in tuning the performance (may be solstice or any other 
stuff).




Responses:


Karl Vogel


Do you have the Oracle binaries, database files, and logging files all
   on separate physical drives?  That would definitely help.

   Mount some or all of your drives with the "noatime" and "logging"
   options.

Rami Aubourg

Could you check whether the slow I/O occurs solely on Oracle writes? Do a 
plain ufs copy and see whether you've got the same problem. You could check 
the write speed with iostat -x 2.
I've myself had some weird I/O performance trouble with Oracle and recent 
Sun Hardware (S1 bay, Sunblade 1000 fiber channel disks). Can't get over 
1.5MB/s write with Oracle, though plain ufs writes are fine. On older 
hardware (A1000 ultra SCSI2 bay) and Sunfire V100 IDE disks, I get max 5-6 
MB/s I/O with Oracle.

The problem comes from Oracle dbwriter process waiting for up to 800ms for a 
response from underlying filesystem (ufs). Dbwriter uses asynchronous I/O. 
The logwriter process, which uses sequential I/O, doesn't have this problem. 
We've been looking at this for about a month with our Sun reseller, and for 
a week now with Oracle support. No solution so far.



Kevin Buterbaugh

I'd recommend picking up a copy of "System Performance Tuning" (2nd
edition) by Musumeci / Loukides, published by O'Reilly, and reading the
I/O related chapters (read the whole book!).  It's much more up to date
than Adrian's info.

     Some general things to check on:  1) how is your data laid out?  2)
Are you using raw devices or filesystems for your Oracle data?  3)  What
type of RAID are you using?  RAID 5 in software is horrible for write
performance.  RAID 0+1 is much better.  HTH...

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