Re: How fast should an IO be on a SYMMETRIX?

In article <bnm13d$lnd$2$8300dec7_at_news.demon.co.uk>, Jonathan Lewis wrote:

> 1) "Virtualization layer" - a marketing term for a black box with
> another layer of software introducing another overhead

This has nothing to do with marketing. It *is* another layer. That layer isn't there to provide overhead - it's what makes those kinds of storage systems fast. Note that I'm talking about the cache here, and the way how it's used (on a Symmetrix). No host ever gets to talk to a real physical drive.

> 2) I thought the benefit of a 'virtualization layer' was that
> you didn't need to know what was going on underneath !

Well, you thought wrong. :-)

After built-in caches were added to standard harddisks, it was still just as useful and necessary as before to know how things worked 'underneath' the cache.

> 3) I quite agree with your final point - you certainly should make
> sure you have the knowledge required to minimise the problems
> inherent in running Oracle databases on a relatively small
> number
> of big discs. James Morle's paper is a good starting point.

Not only 'minimise the problems'. A thorough understanding of the system you're using (on *every* layer) will provide more benefits that just minimise problems. For starters, you won't be dealing with a black box. :-)

I'll read the paper you mentioned.

-- 
Jurjen Oskam

PGP Key available at http://www.stupendous.org/