On Sun, Apr 01, 2012 at 01:10:18PM -0500, Mike Miller wrote:
> 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.
>
> $ 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
                                          ^^^^^^^

It seems that you have two RAID devices, md0 and md1, each supported
by one partition on sda.  There is no other physical disk present, so
the arrays are in degraded state.  They 'work', but only one disk is
present.  You have no protection.  You have no second drive.

Cheers,
florin

-- 
Beware of software written by optimists!
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