Re: Performance Question: RAID or Individual drives ?

That was well timed - I'm just in the middle of benchtesting strip v non-strip v single disk v RAID5 for a client. It's a UNIX box, but the outcome *should* be similar on NT. However, *test* you own kit with a mix of the types of transactions *you* are going to perform. Anyway, here goes (35,000,000 row test table):

READING: One disk, best read rate 10MB/s per disk (one of).

3 striped disks, 3.4 MB/s per disk. If parallel query used (degree of 2 or 4), rate goes to 5.7 MB/s per disk. In other words, if you stripe (64k), it's also best to use parallel query when you can, because if you don't you won't max out the I/O bandwidth you've created.

On 6 striped disks, 1.95 MB/s per disk. With degree of 2 or 4, 4.4 MB/s per disk. In other words, still use parallel, and although you continue to get a boost, it's reducing.

RAID5 - 1 processor, 8.3 MB/s per RAID set. Parallel with degree of 2 or 4, 16.9 MB/s per RAID set. In other words, for reading, RAID5 is just as quick as striped disks, but you still need to go parallel to max out the I/O. And, of course, RAID5 (like striping) is much faster than non-RAID single disks, as long as you can provide the CPU to drive it.

WRITING (in summary as I haven't finished yet):

3 striped drives are about twice as fast as a single disk (not three times faster).
6 striped drives are about 4.5 times faster than a single disk. NB. Like reading, the overhead of sync'ing the drives, memory bandwidth, etc., affects how much real improvement you get - it won't be linear as you add more drives.

RAID5 - on my limited testing so far, writing (creating a 4 Gig tablespace) has dropped from 3 x 6.8 MB/s per disk to 7.5 MB/s per RAID set. In other words, RAID5 array is over twice as slow on heavy writing as the same disks striped (non RAID5).

In summary, look at striped disks (RAID0 or RAID0+1 or through an LVM) for write intensive parts of your db. Look at RAID5 for read intensive sections, and learn to live with the write penalty where you can.

MotoX.

Dominic Baines wrote in message <35AA0A1F.41151B15_at_hermes.cam.ac.uk>...
>I've an NT admin who RAID's everything on every NT box he touches. This
>is OK for redundancy if the system dies but I'm not sure this is the
>best option for an Oracle database performance reasons mainly. Are there
>any tuning guru's out there who could shine a like on the appropriate
>arguament to use IF it would be better to use individual drives rather
>than to rely on the RAID set ?
>
>What am I talking about ?:
>
>Standard set-up would be an Oracle server on NT 4 SP3 with system disk
>a mirrored pair and second 'drive' being a raid set over say 7 to 15
>disks. So ORANT is on D:, as is everything else. OK there are different
>drives and spindles but every read or write to anywhere on the RAID set
>would use every drive, wouldn't it ? These are 4GB Seagate SCSI drives.
>The controller is a proper RAID controller, whatever that may be. It's
>all on Compaq kit.
>
>Thanks,
>
>Dominic Baines
>
Received on Mon Jul 13 1998 - 09:36:26 CDT