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Redo and Archive Log Question

From: Chuck <ccarson_at_echeeba.com>
Date: Thu, 06 Mar 2003 23:14:40 -0800
Message-ID: <3E6846E0.7040708@echeeba.com>

We are trying to add some more redundancy to a very busy OLTP database and I have this question.

I currently have 4 dedicated logging disks as follows:

disk 1 = control01.ctl, redo1a.log
disk 2 = control02.ctl, redo2a.log
disk 3 = control03.ctl, redo1b.log
disk 4 = redo2b.log
disk 5 = archive_dest_1

These 5 'disks' are all RAID 0+1 volume groups on an IBM SAN. (18Gb 10k rpm) I want to add another logging disk which will be on another SAN Switch/RAID Controller, in order to protect against failures in our Brocade Switch or IBM FastT controller. (We have two independent SAN's)

disk 6 = redo3.log, archive_dest_2

Disk 6 is a larger, slower disk (70 Gb 10k rpm) that will also have more I/O contention than disks 1 - 5. (due to redo and archive on the same disk)

My questions are:

  1. If I have 3 copies of each online log file (as configured above) but one of the copies is on a slower disk (disk 6), will the slower disk be the 'weakest link' so to speak. OR, can the ARCH process start archiving the first full online log written within the group even though the third member may be lagging behind due to poor I/O?
  2. Same thing as question 1, but applied to the archive process.
  3. Can I have a third group with only one member even though the first two log groups have two each?

I hope this makes sense, it has been a long day.

Thanks,
Chuck

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