Re: Redo and Archive Log Question

Chuck <ccarson_at_echeeba.com> wrote in news:3E6846E0.7040708_at_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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Yes, the slowest logfile group member will be the bottleneck. Archiving cannot start until the log group is "closed out" during a log switch (meaning all I/O is complete, etc).

More importantly, a slow logfile member may impact runtime database performance, depending on disk controller queues, etc...

Rick Received on Fri Mar 07 2003 - 05:25:02 CST