Re: MIRRORING DILEMMA
1999-11-02 19:14:55
At 05:47 PM 11/2/1999 -0500, William Dias wrote:
[...]
>AIX Mirroring:
> To do proper AIX mirroring you should have three or more drives.
This
> is
>because AIX requires 51% of the drives to be online to do a write.
Clearly not true. A volume group requires 51% of the drives to be online
in order for the volume group to be online, unless it is a non-quorum
volume group. However, the volume group being online has nothing to do
with mirroring. You can have tons of disks in the volume group, yet still
have a logical volume mirrored on only 2 disks. The 51% rule has nothing
to do with being able to do writes.
> For the ADSM recovery log we use only two drives.
This depends on your configuration. You can have lots of recovery logs,
and ADSM can support up to 3 copies of each log volume.
> If ADSM can not write to the recovery log it
>will abort without changing the database. AIX mirroring allows you to
write to
> one drive and at the same time read from the other. This gives you the best
>performance, but requires twice the disk space.
Twice the disk space as what? non-mirroring? It's the same amount of disk
space whether you mirror in AIX LVM or in ADSM.
>RAID5 Mirroring:
>The ECC only adds about 20% to the total disk space required.
Depends on your raid configuration.
> AIX mirroring adds 100%.
True, as does ADSM mirroring.
>Because you are using all the disks together you can not read and write at
the same time. Because the disk motors run
>at slightly different speeds the read/write operations will start and end at
>different times for each disk. This makes for slower disk operations.
RAID 5
> is slow, but cheap.
But you didn't mention write-cache, which offsets most of the performance
penalty.
..Paul
--
Paul Zarnowski Ph: 607-255-4757
Paul Zarnowski Ph: 607-255-4757
747 Rhodes Hall, Cornell University Fx: 607-255-8521
Ithaca, NY 14853-3801 Em: psz1 AT cornell DOT edu
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- Re: MIRRORING DILEMMA, William Dias
- MIRRORING DILEMMA, Valles, Raul
- Re: MIRRORING DILEMMA, Remeta, Mark
- Re: MIRRORING DILEMMA, Richard Sims
- Re: MIRRORING DILEMMA, Adam Slesinger
- Re: MIRRORING DILEMMA, Julie Phinney
- Re: MIRRORING DILEMMA, Valles, Raul
- Re: MIRRORING DILEMMA, William Dias
- Re: MIRRORING DILEMMA,
Paul Zarnowski <=
- Re: MIRRORING DILEMMA, Paul Fielding
- Re: MIRRORING DILEMMA, William Dias
- Re: MIRRORING DILEMMA, Remeta, Mark
- Re: MIRRORING DILEMMA, William Dias
- Re: MIRRORING DILEMMA, Richard L. Rhodes
- MIRRORING DILEMMA, Valles , Raul [mailto:rrv3
- Re: MIRRORING DILEMMA, Richard Sims [mailto:rbs
- Re: MIRRORING DILEMMA, William Dias [mailto:wdias
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