We are also in the paranoid category.  We use TSM to mirror both log
and database, each of which are on RAID5 arrays (each array connected
via separate HBAs).  We have seen failures that have resulted in data
corruption on RAID5 arrays (various vendors and causes), fortunately
not on our TSM server, but on other servers.  This type of failure is
not protected by storage device mirroring or RAID protection, but
should I think be protected by TSM mirroring.  RAID5 provides nice
protection against media failure, and we like the hot spare
replacement that such arrays provide.  It makes handling such
failures very easy.  And, while database backup and roll-forward log
recovery can provide similar backup coverage for array failure, our
database is so large that we feel a second copy is warranted.  It
provides us ride-through protection in the event of virtually any
type of disk failure.

Our DB and LOG volumes are currently on IBM DS4000.

..Paul

At 04:06 PM 9/1/2005, Tae Kim wrote:

Hello all, I wanted to know what your thoughts are on Mirroring DB or Log
volumes that resides on a storage sub system (ESS, EMC, HITACHI).  They
are all supposed to be redundant enough to be up 99.9999% of the time with
proper server configuration (multi path to multi fibre HBA) do you guys
see the need the mirror your DB and Log volumes?

Tae Kim

McKinsey & Company
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New York, NY 10022
(212) 415-1724
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--
Paul Zarnowski                            Ph: 607-255-4757
Manager, Storage Systems                  Fx: 607-255-8521
719 Rhodes Hall, Ithaca, NY 14853-3801    Em: psz1 AT cornell DOT edu