Re: Upgrade to big SUN box or RAC for data warehouse?

"Tanel Poder" <tanel@@peldik.com> wrote in message news:<3f1d9a46$1_1_at_news.estpak.ee>...
> Hi!
>
> No, 2 phase commit is used in transactions distributed between different
> databases.
> RAC doesn't increase IO per se, but it allows to overcome CPU (and memory)
> bottleneck, thus allowing more IO to be done. But since you still operate
> with the same number of disks, they can't service any more IO requests. A
> disk with average 5ms seek time can service 20 IO requests per second, but
> if you got more and more requests coming, they will queue up and the queues
> will grow until you start having problems such are IO timeouts etc..
>
> Tanel.

Tanel,

bad math.
5 millisecond average seek time translates into roughly 200 I/O request per second, not 20 - but not really. depending upon scatter and access patterns - the drives may handle greater or fewer requests per second.

at best, if the blocks requested are on the same track, the average latency is one-half of a rotation, which is inversely proportional to the drive rotation speed. at worst, the blocks requested a a full stroke seek across the platter plus a full rotation. check out storagereview.com for explanations.

Paul

>
> "Ryan" <rgaffuri_at_cox.net> wrote in message
> news:PTfTa.875$5b7.404_at_lakeread01...
> > why would implementing RAC increase I/O? is that because of the 2 phase
> > commit? So you have to write to multiple datafiles?
Received on Wed Jul 23 2003 - 11:24:57 CDT