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itnaa 07-25-2007 10:03 AM

Crash & Subsequent RAID Rebuild
 
Hi Folks,

Would appreciate help in understanding the process of a RAID rebuild after a crash. The RAID setup I have mirrors disks, and I have hardware RAID.

What happens after a crash?

-- The system reboots & I respond by a 'yes' for filesystem integrity check
-- The filesystem check complete (it seems to dump to lost+found), the server finishes booting
-- At this stage, the RAID rebuild kicks in ...

Question:
What is being rebuilt? The image before the crash or the image after the filesystem integrity check?

To be sure, call my mirror set d0 & d1. Assume(?) that d0 is used to boot off, and RAID images d0 onto d1. All fine, until a crash. Now presumably, d0 is corrupt and due to the crash d1 hasn't had time to image d0. So now I reboot, and the OS does a file system integrity check on d0 & fixes any problem it finds. That done, system completes the boot process off d0. Now we have a state where

d0 = crashed & repaired OS
d1 = before crash OS

at this stage, what does RAID do? d0-->d1 or d1-->d0 ?

I suspect it is d0 --> d1, since one must assume that d1 mirrored whatever it was that corrupt the OS.

Just want to be sure of my understanding, and that I'm not overlooking any other possibility. Thanks.

macemoneta 07-27-2007 12:02 AM

There is no master in a RAID-1 mirror. Whichever drive dropped out of the array is the destination of the sync. A RAID-1 sync copies all blocks from one drive to the other to create the mirror.

itnaa 08-14-2007 12:29 PM

Thanks macemoneta.


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