Re: Re: RAID 5 vs RAID 0

In article <A3C801763DAFD411A57900508B9AAF972922_at_HEARTOFGOLD>,   kfrendo_at_bvb.gi (Kelly-Anne Frendo) wrote:
> From Sybrand Bakker's mail,
> "Main conclusion : don't put redolog files on RAID 5"
>
> However, I do not understand why not.
> Can anyone explain this to me?
> Thanks
> K.
>
> --
> Posted from stan.gibnet.gi [195.166.192.3]
> via Mailgate.ORG Server - http://www.Mailgate.ORG
>

Hi Kelly,

This is because of the write penalty associated with RAID-5. For each write a CRC has to be calculated. The CRC is written on disk too, the CRC is read back on disk, and compared with the value in memory.
All transactions are written to redolog files *before* they are written to the database. Redologfiles are being written continuously, and sequentially. If the performance of redolog writes is insufficient, this will ultimately slow down the *complete* database.

Hth,

--
Sybrand Bakker, Oracle DBA

All standard disclaimers apply
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