Thanks for all the responses. A little more digging revealed: md0 is made up of two 250G disks on which the OS and a very large /var partions resides for a number of virtual machines. md1 is made up of two 2T disks on which /home resides. Challenge is that disk 0 of md0 is the problem and it has a 524M /boot partition outside of the raid partition. My plan is to back up /home (md1) and at a minimum /etc/libvirt and /var/lib/libvirt (md0) before I do anything else. Here are the log entries for 'raid' Dec 1 20:50:15 desk4 kernel: md/raid1:md1: not clean -- starting background reconstruction Dec 1 20:50:15 desk4 kernel: md/raid1:md1: active with 2 out of 2 mirrors Dec 1 20:50:15 desk4 kernel: md/raid1:md0: active with 1 out of 2 mirrors This is a desktop, not a server. We've had several short (<20 sec) power outages over the last month. The last one was on 1 Dec. I suspect the sudden loss and restoration of power could have trashed a portion of disk 0 in md0. I finally obtained an APC UPS (BX1500G), installed, configured, and tested it. In the future, it will carry me through these short outages. I'll obtain a new 250G (or larger) drive and start rooting around for guidance on how to replace a drive with the MBR and /boot on it. On Wed, 2014-12-03 at 22:11 +0100, Leon Fauster wrote: > Hi David, > > Am 03.12.2014 um 02:14 schrieb David McGuffey <davidmcguffey at verizion.net>: > > This is an automatically generated mail message from mdadm > > running on desk4 > > > > A DegradedArray event had been detected on md device /dev/md0. > > > > Faithfully yours, etc. > > > > P.S. The /proc/mdstat file currently contains the following: > > > > Personalities : [raid1] > > md0 : active raid1 dm-2[1] > > 243682172 blocks super 1.1 [2/1] [_U] > > bitmap: 2/2 pages [8KB], 65536KB chunk > > > > md1 : active raid1 dm-3[0] dm-0[1] > > 1953510268 blocks super 1.1 [2/2] [UU] > > bitmap: 3/15 pages [12KB], 65536KB chunk > > > the reason why one drive was kicked out (above [_U] ) will > be in /var/log/messages. If it is also part of md1 then > it should be manually removed from md1 before replacing the > hd. > > -- > LF > > > > > > _______________________________________________ > CentOS mailing list > CentOS at centos.org > http://lists.centos.org/mailman/listinfo/centos