Oracle-L: S.A.M.E

From: <Rajesh.Rao_at_jpmchase.com>
Date: Mon, 12 May 2003 14:26:43 -0800
Message-ID: <F001.0059739A.20030512142643@fatcity.com>

Have been trying to understand S.A,M.E. I am sure this must have have been debated earlier on this list. How do I access and search the archives for it?

Some of the salient points of S.A.M.E, as I try to understand it :

SAME aims to spread disk I/O across all the available disk drives, and thus reduce the length of the disk queues. You dont have to worry if its an OLTP, or a datawarehouse. It is used when you cannot accurately predict the I/O requirements of your datafiles, and if the I/O loads are not too demanding. The NVRAM cache will cover up most of your wrongdoings.

SAME recommends not to sepearate DATA and INDEX tablespaces. It is recommended that even Redo and Archive logs be stripped across all the disk drives. While this can increase response time when different jobs access the same disk, this is alleviated by the additional bandwidth, and reduced queuing.

A disadvantage mentioned is that adding new disks could mean restripping the database, unless the disks are partitioned, and these partitions can be moved to the new disks. "Sliding the Stripe".

Some general recommendations made in the paper (not necessarily related to SAME, I believe) are:

For better sequential bandwidth, A stripe width of 1Mb will reduce the seek times, and is strongly recommended. Ensure Oracle issues large I/O calls.

So,If I have a block size of 8K, does it mean that I should set db_file_multiblock_read_count to 128?

2. To reduce the seek overhead during random access, Heavily accessed files should be placed on the outside half of the disk drives.

Your comments on this would be greatly appreciated. Any other positives or negatives of the S.A.M.E approach? Do the Gurus recommend it?

Regards
Raj

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