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Old 10-31-2009, 06:18 AM   #1
Registered: Jan 2009
Location: Dhahran, Saudi Arabia
Distribution: RHEL 5
Posts: 42

Rep: Reputation: 17
Reassembling a raid device


I have a question that has been puzzling me since last night. I had a raid device /dev/md0 configured with raid 1 ( two devices). I stopped the array (mdadm -S /dev/md0).. If you look at /proc/mdstat, the device is not active, nothing in there.

So, To assemble the array, I did:

mdadm -A /dev/md0 /dev/hda6 /dev/hda7
The raid device is now assembled and active.

The question is: how could linux have known about what the raid level is and other raid configuration given that I had no raid configuration file?

I was thinking that such data is stored on the disks somewhere! or something like that.

Could someone help figure this out?
Old 10-31-2009, 06:08 PM   #2
Registered: May 2004
Location: Amsterdam, Holland
Distribution: Ubuntu, Redhat, Angstrom (others in the past)
Posts: 34

Rep: Reputation: 22
This information is kept in a small block of meta information at the start of members of a raid set. Read about it in the good old software raid howto:

.. and there's an entry here:

Old 11-01-2009, 04:21 AM   #3
Registered: Jan 2009
Location: Dhahran, Saudi Arabia
Distribution: RHEL 5
Posts: 42

Original Poster
Rep: Reputation: 17
Thanks alot Bert. It all boils down to "persistent blocks" on raid members!



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