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I setup a software RAID 1 on a Redhat server, everything went sweet and it synced the first time. The other day the raid failedover for some reason and the disks hadn't been syncing since that first time, so it went back to 2 weeks ago when we did the first sync. We got the system back up running off the master only.

However what would cause the software raid to not sync? I used mdadm to setup the RAID.

Any ideas?

EDIT: Sorry I don't have the output from /proc/mdstat before the raid failedover, it is now running on only the master... I can put the slave back in no problems but I was wondering how to make it sync all the time instead of only when I add it.

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You don't happen to have the output from catting /proc/mdstat do you? –  Matt Simmons Dec 13 '09 at 5:42

2 Answers 2

I've had this happen before.

First, check /proc/mdstat and the system log files for any details.

If the drive seems good you can force it to re-join the pool by doing something like:

mdadm /dev/md0 --re-add /dev/sdb
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A md-device in Linux (Software RAID) will sync all the time, if it doesn't something is wrong.

You don't want it to automatically re-add a failed disk. The disk is being removed from the array because something could be wrong, that can be a read/write error or something else. Check your system log to investigate what is going on and resolve the problem. When you have resolved the cause of the disk being removed from the array, try to re-add it and start rebuilding.

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