Richard Elling - PAE wrote:
This question was asked many times in this thread. IMHO, it is the
single biggest reason we should implement ditto blocks for data.
We did a study of disk failures in an enterprise RAID array a few
years ago. One failure mode stands heads and shoulders above the
others: non-recoverable reads. A short summary:
2,919 total errors reported
1,926 (66.0%) operations succeeded (eg. write failed, auto reallocated)
961 (32.9%) unrecovered errors (of all types)
32 (1.1%) other (eg. device not ready)
707 (24.2%) non-recoverable reads
In other words, non-recoverable reads represent 73.6% of the non-
recoverable failures that occur, including complete drive failures.
Does this take cascading failures into account? How often do you get an
unrecoverable read and yet are still able to perform operation on the
target media? Thats where ditto blocks could come in handy modulo the
concerns around utilities and quotas.
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