Re: Raid performace issues (Raid 5 vs. Raid 0+1) with database files

In article <37cc2e30.107835898_at_news.earthlink.net>,   andreyNSPAM_at_bookexchange.net (NetComrade) wrote:
> Hi folks,
>
> We are thinking to place one of our DB's on a Sun Storedge 5200 and
> Sun Enterprise 4500.
>
> Since we have a web-based OLTP environment, well, actually mixed,
> since we have major updates running at nights against most of the
> data, I thought that RAID-5 is not great, since during the day there
> are a lot of small reads/writes.
> I was thinking about 0+1 on datafiles with actualy data, but I am not
> sure whether I need to mirror the TEMP tablespace or whether I should
> place the REDO logs on the mirror.
>
> Any advice would be appreciated.
>
> Thanx
> ---------------
> Andrey Dmitriev eFax: (978) 383-5892 Daytime: (917) 373-5417
> AOL: NetComrade ICQ: 11340726 remove NSPAM to email
>
>

I have done many many many tests of RAID 5 versuses RAID 1 versus RAID 0+1 (or Raid Ten as I call it). Personally, I have yet to see RAID 10 not offer SIGNIFICANT performance gains in both read only and especially in large update environments. I have used vendor DASD and shared DASD such as EMC. Even with the big EMC cache, RAID 5 smells for a DB server.

The MINUMIM I have seen is a 30% gain in a read only environment on some selected queries when the moon was in the right phase. I have seen it go as much as 1800%. I had to redo this one several times to validate my numbers because even I did not belive this dramatic a gain, but i did it several times. (This was in a Sybase world)

Lots of people use RAID 5 and think it's great and I can envision that there are a small percentage of cases where it will do ok, but..... For the price of today's DASD why cut corners and create unnecessary headaches for yourself and your customers? Do it right the first time and go RAID 10 all the way. IMHO.

Your milage may vary.... Use a performance tool to see for yourself. If your reads are 5-8ms and writes are 5-12ms you are in great shape. However if you are seeing 20, 30 , 50 , 100, 500, or (i saw this) 1500 ms, change to something else.

Also
- If you are mirroring, there is really no reason for multiple redo log members in the groups.
- But archive redo on fast drives.

Good Luck

Doug Coan
Senior Client Server Systems Integrator Aegon USA

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Share what you know. Learn what you don't. Received on Wed Sep 01 1999 - 13:24:22 CDT