Re: Performance Question: RAID or Individual drives ?

Thanks MotoX:

Following you're advise I tried this on a separate server with an almost identical datbase (export of original and imported onto the other) but this time used the 15 drive model for the database (DBA handbook rough example followed) but with the drive non-RAID'd and the performance was just so much better than the RAID5 version for both READ's (about 85% slower) and WRITE's (more than 55% slower). OK so that doesn't tell me much more that I expected really but is there a way to improve the RAID performance ?

I believe the RAID set is one where every drive is striped across every disk and there is a parity member and there is a standby disk. RAID 5 ?

The database (other than system, rbs, temp, tools etc) is 4 data tablepsaces (c2.5GB each) , 4 index tablespaces (c1.6GB each) something like 10,000,000 rows in 250 tables. As you can tell there is plenty of space and it is possible to put one tablepsace on each drive (15 of them) and to separate the software and redo logs etc....

I tried a number of selects and joins, inserts, view creation, timed an export on both !!,

I didn't keep detail figures as the tests were done by hand and I'd like to script it if possible. How would I capture the time taken for each process realistically ? I tried this as a rough stopwatch exercise from a sql*plus connection at both the server and at a client workstation.

At the end of the day I suppose it is the client and SLA's that will win on a recovery arguament rather than performance and as we both answer to the same person they will have to make a choice. The database is approximately 50/50 read/write and it is growing at the rate almost across every tablepsace of some 15% per year in size.

Regards,

Dominic

MotoX wrote:

> 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 Tue Jul 14 1998 - 05:08:17 CDT