Re: external storage and commit?

Sean M <smckeownNO_at_BACKSIESearthlink.net> wrote:
>Tim Smith wrote:
>>
>> For external storage, such as an IBM ESS(Shark) am I correct in
>> saying that a transactions may be written to the ESS cache and not
>> written to disk?
>
>I'm not explicitly familiar with ESS hardware, but from what I've read
>it works very much the same as other popular (i.e. EMC) disk
>subsystems. In which case, yes, this is correct.

This is also true of HP XP series arrays, they term it a "cache lun". If you generate sufficiently little redo, and can spare a few GB of the array cache for it, it works very well. Certainly the Shark has the required battery-backed, mirrored RAM.

Even though it should work in theory, I'd explicitly check with Oracle or IBM that the configuration is supported.

In the sort of systems I'm involved with, using the array cache for redo isn't that useful, as it is too small and leads to too frequent checkpoints. Someday somebody will give me 100GB of solid state disk for my online logs, and I'll be happy, and wave goodbye to log buffer and log sync waits. :-)

-- 
Andrew Mobbs - http://www.chiark.greenend.org.uk/~andrewm/