Re: Performance Question: RAID or Individual drives ?

Art S. Kagel wrote in message <35AA596B.464F_at_bloomberg.net>...
>That said Motox is
>right about the write penalties of RAID5. However, he did not seem to
>test the best configuration of all for databases: RAID10 or 1+0 as
>Sergei mentions, which is a stripe of mirrored pairs.

Correct, but the SSA adapters I was testing in this case do not support RAID0 or RAID1 - only RAID5. Mirroring can be done via an LVM. I should have mentioned this in my post.

>
>We use a 30 drive stripe spread over 4 Ultra Wide/Fast controllers and
>get 30MB/s write throughput for write with 50 processes WRITING to the
>array, read throughput is much higher! Each process, obviously, is
>seeing much less throughput than that (about on a par with Motox's
>testing, but adding more and more processes continues to increase total
>throughput; I just gave up testing when our performance goals were
>surpassed. This is exactly the behavior that one gets with modern
>database parallelization such as Oracle and Informix provide.

Not for a distribution of many, small random I/O's. Striping can actually make things worse. And in those processes are each requesting data from completely different areas of the RAID set - even sequentially - things can still get worse. That's why it's so important to test you own system with your own transactions, as I mentioned to the original poster.

>It looks to me like Motox's testing is using a single Wide or Fast only
>controller and is hitting his controller's I/O limit (10MB/s).

Nope, SSA. 4 x 20MB/s ports, 2 loops, per adapter.

MotoX. Received on Tue Jul 14 1998 - 02:13:39 CDT