I'm not sure what you mean. Do you mean that a host is direct connected instead of through switches ? In that case direct I/O means a host is directly attached tp Clariion's SP ports.

Please be more specific: where did you see the phrase "direct I/O" ?

I would say true in almost all cases except for when highest bandwidth needs to be achieved. Without the write cache over twice the write bandwidth can be achieved but requires some seriously large sequential IO hitting the FE ports and pretty much dedicating the storage array for that one purpose¿

Message was edited by:
calle

Or maybe you mean that when the write cache is disabled, servers are writing directly to disks?
Easy to set up (Properties of the CX3 in Navisphere) but not advised concerning performances!

Thanks for all your answers,
In fact the DBA asked me to configure the CX with direct I/O for oracle
RaidGroups and no direct I/O for users Raidgroups for performance purpose.
I don't know how to set it.
Regards
Consty

I am guessing that your DBA does not know a whole lot about storage networking and storage arrays? I don't think Direct I/O has anything to do with the storage array.

I thought that Direct I/O was an operating system setting. See this link for more details on the Oracle setting:

http://www.ixora.com.au/notes/direct_io.htm

Interesting!
I have seen a cache issue on CX3-80 when restoring data from a new tape. The throughput was so heavy that global write cache was too loaded. We tried to disable the write cache for the LUN on which we were restoring data, and the speed was a bit lower but not so much
But the raid group was not dedicated to this server.

It seems that this DBA asked the wrong guy. He should have asked the operating system guy.

Thanks for all your answers,
I'll check it again because it is confusing.
We talked about operating system parameters ..
Consty

It is definitely an operating system parameter. There is no option for Direct I/O on the storage array.

Could you please set this question as answered and reward points if you think this would be appropriate ?