[CentOS] what is RAID "background initialization" ??

Thu Aug 20 14:33:14 UTC 2009
mcclnx mcc <mcclnx at yahoo.com.tw>

we have DELL server (CENTOS 4.X) with MD1000 connect on it.  One of Raid5 (internal 4 disks) has hard disk bad and I replace it.  I saw /var/log/messages have following entry:

=======================================
Aug 18 15:33:20 host1 Server Administrator: Storage Service EventID: 2049  Array disk removed:  Array Disk 0:11 Controller 1, Connector 0
Aug 18 15:34:09 host1 Server Administrator: Storage Service EventID: 2052  Array disk inserted:  Array Disk 0:11 Controller 1, Connector 0
Aug 18 15:34:09 host1 Server Administrator: Storage Service EventID: 2065  Array disk Rebuild started:  Array Disk 0:11 Controller 1, Connector 0
Aug 19 00:42:58 host1 Server Administrator: Storage Service EventID: 2124  Redundancy normal:  Virtual Disk 0 (Virtual Disk 0) Controller 1 (PERC 4e/DC)
Aug 19 00:42:58 host1 Server Administrator: Storage Service EventID: 2092  Array disk Rebuild completed:  Array Disk 0:11 Controller 1, Connector 0
Aug 19 00:45:53 host1 Server Administrator: Storage Service EventID: 2127  Background Initialization started:  Virtual Disk 0 (Virtual Disk 0) Controller 1 (PERC 4e/DC)

=============================================

My questions are:

1. why after "disk rebuild" there have "background initialization"?

2. is all kind of configuration (e.g. RAID0, RAID10, ...) need perform "background initialization"?

3. if I run heavy application, will it hurt "background initialization" and "disk rebuild"?

Thanks.


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