Hi,
What are the initial checks needs to be done while observing hard errors on one of the hard disk drive.
Thanks,
Babu.
At first you will see error messages via "dmesg" command.
I think good practice is to attach new drive as soon as possible and move data from the failing device rather soon, than too late.
After that you can unmount old device and try "fsck" for errors, alternatively "format -> analyze" for surface test.
In care that disk is part of mirror everything is much more easier.
Anyway disks are expandable properties and doesn't make sense to waste of time by efforts to save them.