Re: I/O Performance/bottlenecks on EMC Symmetrix

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Hi Don,

wait_events that are dominant.
db_file_scattered_reads, db_file_sequential_reads, db_file_parallel_write,sort_segment_request are the dominant wait (right under SQL*Net message from client & rdbms ipc message)
So yes I know I have an I/O problem. It's just that I'm stuck with an EMC storage solution that I can not look into. I need "evidence" to go to SA/management and say that disk layout is no good or something along that line.

I do know for a fact that each individual disk is 36Gb and sliced in (i believe) 4,5Gb slices. You can therefore be sharing disks with other I/O intensive apps.

As for monitoring tools, I'm the lowly DBA that has no business on UNIX so I need the UNIX people to do this for me. They will help as they are always cooperative, but also very busy, so I need to show them some facts and figures.

TIA Jack

"Don Granaman" <granaman_at_home.com>@fatcity.com on 14-09-2001 10:20:17

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> The other workload I would say was about the same (Relatively speaking)
> Both machines did have idle time on the CPU (I/O intensive job).

What are the dominant wait events - in Oracle? It sounds like its probably I/O,
but you might want to verify - if for no other reason than to have some proof to
justify some EMC time and/or a Sym reorg.

> The quicker test machine was a bit stretched on memory at the time
(running
> about 8 databases) but not too bad.
>
> The only thing I can think of is pi** poor performance (3 p's you don't
> want in marketing) of the symmetrix disks.
>
> One point this symmetrix is loaded with 36 Gb disks and all of them are
> sliced to pieces and than allocated to filesystems. In theory you can be
> sharing disks with other high I/O apps (E-mail system etc..).

If this is more than just theory, the message from John Hallis most likely hit
the nail on the head. I'll lay odds of 3:1 for disk/cache contention in the
Sym.

> I do not however have any insight in what is where physically.

My condolences. EMC should be able to help here though, if you don't have another way (ecc, DBtuner, etc.). They should be able to come in, look at the
Sym, and tell you what is going on - in cache, against disks, etc. - and also
tell you whether it "should be" a problem or not.

There is a common thread to all these good responses you are getting - I/O tuning is still critical, in spite of any vendor propaganda to the contrary.

-Don Granaman
[OraSaurus - Honk if you remember UFI!]

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