Is this NFS or FC?

By default, Oracle does sequential reads in 1M chunks. If they have a 16k block size on the database, it should be reading in units of 64, not 128. Also, just because Oracle tries to read 1MB chunks doesn't mean the database can do that.

They really shouldn't be using cio as a mount option either. Any remotely current version of Oracle will mount the datafiles with concurrent IO so long as they have filesystemio_options=setall, which is also what they should have.

If you can send me a sample report from 'awrrpt.sql' of no more than one hour elapsed time from a period where they are unhappy with performance, I will take a look and what's going on. I can say with 100% certainty that if they really are doing multiblock reads with 16K units the problem isn't ONTAP. I suppose it could be a 16K block size on a badly fragmented jfs2 filesystem, but I really doubt it. I think something is being misinterpreted.

From: toasters-bounces@teaparty.net [mailto:toasters-bounces@teaparty.net] On Behalf Of Rhodes, Richard L.
Sent: Wednesday, June 29, 2016 4:36 PM
To: toasters@teaparty.net
Subject: OnTap read block size?

OnTap 8.1.2p1

Our DBA's are complaining that our nSeries (N3220/FAS2240) is reading really slow due to it only returning small 16k blocks. The DBA's are saying the Oracle multi-block read ahead should be reading 128 x 16k blocks = 2m read, but it's only seems to be reading/returning 16k at a time.

On a AIX filesystem mounted CIO, if I run

"dd if=/dev/zero of=z bs=1m count=9999"

I see writes of 500k.

In the same filesystem mounted CIO, if I read an existing db file

"dd if=<dbfile> of=/dev/null bs=1m"

I see reads of up to 30k.

Q) Is there a limit in OnTap on read size?

Thanks

Rick

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