Re: Disk mirroring v's stripping

Summary - How do you position Oracle RDBMS files when OS stripping is in effect?

Have the stripes for the Redo logs, control files, and data laid out on different disk volumes is the best way to control this. Also since many if not most shops place both data and index tablespaces on the same disk due to a limited number of disks and then try to place the indexes for a particular table in an index space on a different disk have multiple data and index stripes laid out. Then document this and place your tables and indexes as best you can.

Now OS level stripping in blocks which hopefully match the Oracle block size of your database basically turns all your database I/O into random I/O. This has a tendancy to move your average access time for a physical block of data to the disk average rated access time. However, be aware that sequential reads and processes that consist of mostly sequential reads like imports and full table scans can definitely be significiantly slowed down by stripping. Therefore I recommend that your shop not stripe every file in the system, but only stripe the database files and not your backup file disks.

Note, OS stripping can be done in two ways. The best way is one block at a time on the first disk to the last disk assigned to a stripe then back again for however many blocks make up the stripe. The other way is concatenation of chunks of space on one disk to the space on another disk and so one. This space is written to by the OS from the first allocation to the last. I recommend you not use concatenation.

The shop I am at uses OS stripping and mirroring on a 40 to 50 gig production data base so I can speak from some experience. Also remember that OS stripping can and will greatly increase the total amount of data that must be recovered in the event of disk failure. I believe that mirroring is a requirement if you OS stripping ( I do not mean technically, but a personal requirement)

I hope this is helpful.

Sincerely,
Mark Powell -- The only advise that counts is the advise you follow so follow

• your own advise..