Matthias Urlichs wrote:

In fact, as I said, there may be problems lurking on other disks which I
just haven't found yet (how often do you read all 5TB of your data?),
which means that a feature like this is the difference between being
able to recover and certain data loss, RAID-6 nonwithstanding.

This is why scheduled "check" or "repairs" should be done - see 
Documentation/md.txt in the kernel source for details.

Regards,

Richard