514 IBM Midrange System Storage Hardware Guide
This problem is exacerbated by using large arrays with RAID 5. This stripe kill can lead to
data loss when the information to rebuild the stripe is not available. The end effect of this
issue will of course depend on the type of data and how sensitive it is to corruption. While
most storage subsystems (including the DS5000 storage subsystem) have mechanisms in
place to try to prevent this from happening, they cannot work 100% of the time.
Any selection of RAID type should take into account the cost of downtime. Simple math tells
us that RAID 3 and RAID 5 are going to suffer from failures more often than RAID 10. (Exactly
how often is subject to many variables and is beyond the scope of this book.) The money
saved by economizing on drives can be easily overwhelmed by the business cost of a crucial
application going down until it can be restored from backup.
Naturally, no data protection method is 100% reliable, and even if RAID were faultless, it will
not protect your data from accidental corruption or deletion by program error or operator error.
Therefore, all crucial data should be backed up by the appropriate software, according to
business needs.
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