Re: Configuring for Online Redo Logfiles

Hi Vivek,

If I didn't worry about data safety I would choose redo logs on dedicated single disks.
The reason is that usually the speed of LGWR's writes is more important for performance compared with speed of ARCH's reads.

Regards,
Ed

> Conor,List
>
> 1) Mirrored Redo Logs WRITES may have an Overhead of 15-20 %
> EXCERPT from Gaja's Doc "One of the common myths with mirroring, is that
> it takes "twice as long" to write.But in many performance measurements
> and benchmarks, the overhead has been observed to be around 15-20%."
>
> 2) Mirrored Redo Logs READS are Twice as Fast than NON-Mirrored
>
> Considering BOTH the Above to POINTS , FINALLY Strictly w.r.t.
> performance of Online Redo Logs , WITHOUT any Consideration for Data
> Safety , Which would be Better ?
>
> Thanks
>
>
> > -----Original Message-----
> > From: Connor McDonald [SMTP:hamcdc_at_yahoo.co.uk]
> > Sent: Thursday, November 15, 2001 3:15 PM
> > To: Multiple recipients of list ORACLE-L
> > Subject: Re: Configuring for Online Redo Logfiles
> >
> > An unmirrored disk will run faster (with respect to
> > writes) than a mirrored one (not twice as fast since
> > writes on a mirror are typically done in parallel).
> > Then again - now you've got an unmirrored redo
> > log...not a good idea. To get around this, you'd need
> > to duplex it through Oracle - which pretty much gets
> > you back to a "mirrored" redo log.
> >
> > hth
> > connor
> >
> > --- VIVEK_SHARMA <VIVEK_SHARMA_at_infy.com> wrote: >
> > EXCERPT from "Implementing Raid On Oracle Systems"
> > > by Gaja Krishna
> > > Vaidyanatha, Quest Software Inc. :-
> > > "RAID 1 - Ideal for online and archived redo logs,
> > > Leaves the write-head
> > > at the location of the last write. On most systems,
> > > you will need 3
> > > volumes for the online redo logs (for 3 groups) and
> > > 1 volume for the
> > > archived redo logs. If your database is in
> > > NOARCHIVELOG mode, you
> > > probably can get away with a single RAID 1 volume
> > > for your redo-logs.
> > > However, for databases in ARCHIVELOG mode you will
> > > need to further
> > > separate you"
> > > Qs. Puttting an Online Redo log on a RAID1 Volume (
> > > Volume Containing 1
> > > Disk Mirrored to Another Disk ) versus putting the
> > > Same Online redo file
> > > on a Single Disk (NON-Mirrored) , which would give
> > > Better performance ,
> > > Why ?
> > > --

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Author: Edward Shevtsov
  INET: ed_at_mb.ru

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