[CentOS] [Q} how can O.S. predicate a disk going to failure??

we have CENTOS 4.X on DELL server and one one of virtual disk include 4 disk configure as REID5 (one more disk for hot spare).  I saw /var/log/messages file have:

Aug  4 06:27:02 host1 Server Administrator: Storage Service EventID: 2094  Predictive Failure reported:  Physical Disk 1:5 Controller 0, Connector 1
Aug  4 06:27:02 host1 Server Administrator: Storage Service EventID: 2051  Physical disk degraded:  Physical Disk 1:5 Controller 0, Connector 1

I use DELL OPMN to check and found "disk 1:5" still "online", but "predicate failure".

I also use DELL OPMN to check virtual disk and it show "online", not "degrade".

my questions are:

1. is this disk really "degrade" or not?

2. how O.S. can predicate disk going to failure?

3. do I need replace this disk now?

Thanks.


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