Re: Separating online redo logs from database files
- From: Craig Hagan <hagan@xxxxxxx>
- To: vbarac@xxxxxxxxxxxx
- Date: Thu, 8 Apr 2010 12:31:46 -0400
Much comes down to two issues:
1) performance
the redo log io pattern is often different than the io pattern presented
to datafiles. ideally, you'd want to match storage to that.
2) availability
the redo ultimately can be the life of the db if you can't afford to lose
transactions. For such systems, you ideally want multiple *complete* io
paths for each member (distinct io controller, bus, cables, and arrays).
This is to isolate you from specific component failures and/or problems
which could lead to data being unavailable, or worse, corrupted. By having
the other member(s) using completely different parts, you can overcome such
a failure mode and continue operations and/or successfully recover from the
fault without loss.
On Thu, Apr 8, 2010 at 5:02 AM, Vladimir Barac <vbarac@xxxxxxxxxxxx> wrote:
> Hello, listers
>
>
>
> What are general pros and cons on separating redo logs from database files?
> Both database and redologs are already residing on RAID1 volumes. So this
> separation would only mean – move redo logs to separate mount point (RAID1,
> still).
>
>
>
> We have EMC consultant insisting that it is in line with best practices.
> Why exactly is it a good thing, what "best practice" actually means – he
> can't say.
>
>
>
> Our systems are moderately used OLTP databases. I we had lots of waits on
> redo log writes (and we don’t), I would understand moving redo logs to flash
> drives (for example). Or, as I have seen previously, database goes to RAID5
> and redo logs to RAID1 – depends a lot on database usage, etc. etc.
>
>
>
> Actual real life inputs are welcome.
>
>
>
> Regards,
>
> Vladimir Barac
>
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--
.- ... . -.-. .-. . - -- . ... ... .- --. .
Craig I. Hagan
hagan(at)cih.com
"Tout ce qui est exagéré est insignifiant.": ("All that is exaggerated is
insignificant.")
Talleyrand
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