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I detached one half of my linux md raid1 (--fail --remove) to do some potentially risky filesystem work, to be sure I had a good copy on hand if things went bad. Things went well, and now I want to resync the now out of date half.

Can I just --add it back? is there something I should do to be sure the out of date data is not the copy that will be synced to the rest?

eg. the update time on the one that's currently connected to the array is Update Time : Mon Aug 13 10:49:07 2012, and the update time of the half that is not connected is Update Time : Fri Jul 29 16:45:06 2012. Does this mean it will be synced from the newer copy to the older copy when I reattach the older copy?

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Yes. Add it back and it will resync. You may in the future want to use LVM and do a snapshot (removes the whole resync time, and maintains the integrity of RAID1).

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there's no concerns the old stuff will overwrite the new stuff? – user1238763 Aug 13 '12 at 19:36
@user1238763 No, because the meta-data on each raid partion stores "last update" so the "newer" data is always used as the good data. – utopiabound Aug 29 '12 at 13:08

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