Re: Oracle Performance - RAID vs split tables

In article <936882692.24578.0.nnrp-06.9e98cce4_at_news.demon.co.uk>, Raindrop Support service_@_raindrop.co.uk says...

> However, we have recently been advised by various Oracle gurus that it is
> better for Oracle performance to manually split up the physical locations of
> individual tables, indices and logs across physical disks. This cannot be
> done with RAID. Additionally, we have been advised that RAID5 actually
> *slows down* Oracle.

The reason for splitting up filese over several disks is to spread the i/o. Disk striping (RAID0 and RAID5) does this w/o you having to do this manually. RAID5 however has an overhead when writing and is slower for writes. When you have operations wich involves a majority of writes like writing log files a RAID 5 is slower. RAID5 should theoretically be faster for reads than a single disk, but I have read benchmark report showing that there is no significant difference in speed (I have not tested this so I am not sure if it is correct). If this is true then it would be better to use RAID1.

One configuration I have been thinking of is to use 1 RAID5 for datafiles and other stuff and two single disks for redo logs and archive logs (both mirrored in Oracle). The reason for putting the logs on seperate disk is that those are write intensive and putting them on spearate non-rAID5 disks is to avoid the overhead of write operation on RAID5.

One question is, what will give best performance: for example use a RAID5 with 4 disks or two RAID1 arrays with 2 disks each and manually seperating i/o? My guess is that 2 RAID1 arrays would provide better performance (i.e. if it is possible to know which objects to be placed on which array)

Magnus Received on Thu Sep 09 1999 - 17:43:24 CDT