[tclug-list] testing that RAID1 is working using mdadm

[Mike Miller]

I want to be sure that my RAID1 is working properly.  What's the best way 
to do that?  I tried mdadm --detail (see below) and I guess mdadm thinks 
it is working, but one part surprises me: "Array Size" is different for 
the two disks.  Is that normal?  The disks are two identical 2TB drives.

Mike


$ sudo mdadm --detail /dev/md[01]
[sudo] password for [user]: 
/dev/md0:
         Version : 00.90
   Creation Time : Tue Oct  4 11:45:48 2011
      Raid Level : raid1
      Array Size : 1945312384 (1855.19 GiB 1992.00 GB)
   Used Dev Size : 1945312384 (1855.19 GiB 1992.00 GB)
    Raid Devices : 2
   Total Devices : 1
Preferred Minor : 0
     Persistence : Superblock is persistent

     Update Time : Sun Apr  1 12:54:52 2012
           State : clean, degraded
  Active Devices : 1
Working Devices : 1
  Failed Devices : 0
   Spare Devices : 0

            UUID : d64b75e8:e8767139:e368bf24:bd0fce41
          Events : 0.2357380

     Number   Major   Minor   RaidDevice State
        0       8        1        0      active sync   /dev/sda1
        1       0        0        1      removed
/dev/md1:
         Version : 00.90
   Creation Time : Tue Oct  4 11:46:13 2011
      Raid Level : raid1
      Array Size : 8200960 (7.82 GiB 8.40 GB)
   Used Dev Size : 8200960 (7.82 GiB 8.40 GB)
    Raid Devices : 2
   Total Devices : 1
Preferred Minor : 1
     Persistence : Superblock is persistent

     Update Time : Sun Apr  1 00:57:01 2012
           State : clean, degraded
  Active Devices : 1
Working Devices : 1
  Failed Devices : 0
   Spare Devices : 0

            UUID : 90b1095c:d6dd36a1:e368bf24:bd0fce41
          Events : 0.241

     Number   Major   Minor   RaidDevice State
        0       8        2        0      active sync   /dev/sda2
        1       0        0        1      removed