Re: RAID and Redo Logs

On Sun, 04 Oct 1998 00:03:01 -0600, Brian Yan <by2_at_gpu.srv.ualberta.ca> wrote:

>I was told by a DBA that the disk where the redo log resides should not
>be configured as RAID. Is it true and why? Thank you in advance!
>
>Brian

This is because the redo logs are written to sequentially. While the rest of the database is written to asynchronously, the log files are essentially written synchronously. When a user hits commit, the "transaction committed" message does not get returned until all his data change vectors have been written to the redo logs. Now if you place rdo logs on a RAID5 disk, updates are slower, seek time, maintaining parity checks across disks.... This all slows down what should be fast sequential writes. Even placing redo on striped (no parity) is not advisable because of the increased number of seeks caused by spanning stripes. Ideally the head of the drive sits over the end of the redo writing away. So it's best to keep redo on their own drive with no contentiion.

For resilience use mirroring either thru RAID technology or let Oracle do it for you.

Clive.
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Clive Bostock Received on Sun Oct 04 1998 - 12:28:43 CDT