Re: Cheap RAID system recommendation?

Andrew Mobbs <andrewm_at_chiark.greenend.org.uk> wrote:

>Is that 70MB/s as individual blocks (e.g. typical of many OLTP systems),
>or 70MB/s streaming (maybe in DSS, if you're lucky, on a newly
>installed system, with a following wind)?

It is mainly a DSS application.

>With a typical 15k RPM drive, you've an average seek time of 3.4ms, and
>an average rotational delay of 2ms. The actual time to read a block is
>fairly small.

Yes, and since the actual read and transfer speed has increased much faster than seek speed, doing full table scans becomes more and more attractive.

>At 5.4ms/block that's 185 IO/second - so with 8kB blocks, you'll need
>just over 48 spindles to sustain 70MB/s.

Interesting calculation. It seems that when it comes to DB work, there is nothing more appropriate than a large number of disks. Ideal size: 8 KB per disk :-)

Bye
Rick Received on Mon Aug 19 2002 - 17:54:54 CDT