Data Integrity Validation and Splitting Mirrors

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If the volume is mirrored, and both drives of the mirrored pair incur an irrecoverable

checksum error at the same location, this may be a symptom of various failures:

1. Path problems – in this case, it is typical for there to be multiple reports of

unrecoverable checksum errors in a variety of locations across a variety of files

and tables.

2. Unwritten data – in this case, there may have been some interrupted data load or

restore operation that left the data set incomplete. It is typical for there to be

multiple reports of unrecoverable checksum errors for contiguous sets of data

within the same file.

3. Software problems – in rare cases, software issues may result in a variety of

failure modes that can result in unrecoverable checksum errors.

Data Validation Timing

The data validation can require anywhere from minutes to hours, depending upon the

system load, FCHECK process priority, the RATE used to perform the validation, and the

size of the data set that must be validated. The validation can be performed in parallel

across multiple volumes for each volume subject to a mirror split. The rate at which data

is processed for each volume can range up to 50mbytes/second or more, depending upon

the file set. The best way to determine the data validation timing is with actual experience.

The risk of undetected latent failures is reduced when data is validated prior to splitting

the mirrors. The validation should be performed as close as possible to the mirror split to

ensure the lowest possible risk.