Raid 5 vs mirroring:

Protection against media/drive failure:
  RAID5:
    Protects against single failure in raid group.
    Can be configured with hot-spare, to auto-replace failed drive
    Hot-spare provides failure against second failure, in time
  Mirroring:
    Protects against multiple failures, so long as 2 failures do not
      include both pairs of a mirror.

Performance:
  RAID5:
    Without write-cache, there is a signifcant performance penalty
      using RAID5.  If you have a smallish server, this may not be
      an issue.  As your database gets larger, I/O performance to the
      database may become an issue.
    With write-cache, RAID5 performance approaches non-RAID,
      non-mirrored performance.  Still a slight penalty.  This is a
      rule of thumb and I'm not sure how well it applies to ADSM.
  Mirroring:
    Provides best performance (at least in AIX's LVM, and I >assume< in
      ADSM but I'm not certain).  The reason is that reads are satisifed
      from whichever mirror copy provides the best performance.

Other issues:
  Mirroring:
    Provides the option of mirroring disks using fiber-extended SSA or FC,
    to a remote location.  This enables some DR possibilities.

..Paul
--
At 01:44 PM 4/21/99 +0200, you wrote:
At 01:44 PM 4/21/99 +0200, you wrote:
>Hi,
>
>again I am struggling with my ever growing ADSM DB, not knowing where to
>get the additional disk space I need. An option would be, to give up DB
>mirroring and rely on RAID5 instead.
>
>Since RAID5 protects against media/hardware failures, are there other
>threats, DB mirroring protects against and RAID5 does not? There has been
>discussion on this in August 98 and Andy Raibeck mentioned partial page
>writes. But how probable are they? Has anybody out there ever been in a
>situation where DB mirroring (would have) helped and RAID5 (would have)
>not?
>
>Regards
>
>--
>Reinhard Mersch                        Westfaelische Wilhelms-Universitaet
>Zentrum fuer Informationsverarbeitung - ehemals Universitaetsrechenzentrum
>Roentgenstrasse 9-13, D-48149 Muenster, Germany      Tel: +49(251)83-31583
>E-Mail: mersch AT uni-muenster DOT de                       Fax: 
>+49(251)83-31653
>