Re: spreading disk I/O ,which is better??

Wijbrand Pauw wrote:
>
> Hi,
>
> I have the following problem, I have a heavily used tablespace of 8Gb and IBM
> SSA disks. I can't use logical volume striping.
> I have a choise of making one tablespace on a 9Gb disk or use filesystem
> striping on 4 disks of 2.2 Gb. The last option means making several datafiles
> on the 4 disks. If the last option is the best? and if so, what is wise?
> making a lot of datafiles (say 200Mb each) and file 1-4 on disk 1-4 , file 5-8
> again on the 4 disk's and so on until I have 9Gb or just 4 datafiles on the 4
> disk's .
> Is the choice different when dealing with indexes or tables (indexes tend to
> be accessed more randomly)?
> The disk's are mirrored so reading will be fast but writing will be slower.
> SSA disk's are supposed to be very fast, IBM tell's me a single SSA disk can
> compete with striped FW SCSI disk's. I can make a group of disk's in which the
> other disk's won't influence this disk, so the SSA adapter won't be a problem.
> For people who know SAP , it's the sappcl2 data and index tablespace of the
> payroll.
>
> Thanks for helping!
>
> regards,
>
> Wijbrand Pauw

Wijbrand,

It is always better to place your data and indices in different tablespaces and to place the data files that comprise the tablespaces on different disks, if possible. This will reduce disk I/O contention and should help performance. Since logical striping is not available, as in using RAID hardware, the striping performed by ORACLE is a little more tricky in that you have to set the file sizes so that the 1st, 2nd and consecutive extents are allocated on different disks. Unless you use MINEXTENTS 2 in your creation clause, you won't see any benefit at all until the 1st extent is filled. Each file would have to be slightly bigger than the initial extent to allow for growth.

This method is a little tougher to maintain than logical striping. It is more enforced by the DBA than the Operating System or Oracle.

Hope this helps,

Don Received on Mon Oct 13 1997 - 00:00:00 CDT