How to check whether a RAID array is still consistent?

["Bob" <nospam@nospam.com>]

Hi all,

A few days ago my software-RAID1 array failed because the two disks both had
bad blocks. Probably bad luck, but I find it even more unbeliveable that the
two disks would both fail so shortly after each other. So I suspect that one
of the disks was having problems for some time already but these went
unnoticed because they were covered by the RAID mirroring.

So..: is there a way to periodically check whether RAID disks are still in
sync? Preferable without unmounting the filesystem (similar to the
background rebuilding after adding a disk to an array).

Thanks
Bob