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Re: Any experiences with datafiles on RAID 5 with cache

From: Matthias Gresz <GreMa_at_t-online.de>
Date: Thu, 14 Jan 1999 09:13:01 +0100
Message-ID: <369DA70D.278DC1ED@Privat.Post.DE>

Jarmo Blomster schrieb:
>
> Hi,
>
> Is there any experiences about placing data files (table space+index space)
> on Digital Raid Array 310/3000 with HSZ22 controllers. The RAID level will
> be 5.
>
> To my knowledge there is 16 MB cache available, how much does the cache
> speed up write operations?
>
> How do I estimate the effect of cache in this environment?
>
> TIA,
> Jarmo

Hi,

write cache speeds up write operations that's clear. Oracle itself recommends to turn write cache of since there too many factors that can lead to data inconsistency. As you know putting data into the wirte cache commits the transaction even though data isn't permanent. You may have redudant UPS, batteries to buffer your cache, but would you rely on them? Are you sure that your battery has enough power after system runs for about two years? What about noices on the power lines when switching from commercial power to backup power? Looking at all this factors I decided to switch of write cache. Read cache is a must. The system we got delivered had only 4 MB cache which wasn't enough for Oracle. The two processor spend up their time to fight for that cache so that both ran at 100 % without seeing any progress. The system seemed to be locked up. Encreasing the cache up to 16 MB and finally to 32 MB solved the problem. This costed 100$ at these times, a joke when purchusing a box for 35,000 $.

HTH
Matthias
--
Matthias.Gresz_at_Privat.Post.DE

Always log on the bright side of life.
http://www.stone-dead.asn.au/movies/life-of-brian/brian-31.htm Received on Thu Jan 14 1999 - 02:13:01 CST

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