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MDADM RAID1 of external USB 3.0 Drives



Dear list members,

some time ago, I bought two external Seagate 2 TB USB 3.0 HDDs in order
to expand my local storage (all internal slots are already in use).
Having created a RAID1 with MDADM just as normal, it all seemed to work,
until at one system startup MDADM told me via local mail that the Array
was degraded. In fact, one of the devices had not been recognized by the
system. Reconnecting the drive however, did not allow me to simply
continue as normal -- I had to add the device back into the RAID and
thereby triggered a resync. This did not seem a problem at the
beginning, but as the problem occurred a second time, I thought I should
search for a solution (which did not bring up anything interesting or
related) and then ask:

Is there any means to configure MDADM (or such) to make sure that all
devices are recognized before attempting to start the array so that I
could manually reconnect the missing disk and then start the array
without any resync?

If not, might it be a good idea to write a script to check if the
devices are available and only then enable that RAID?

I want to avoid doing superflous resyncs as this always takes a lot of
time and seems to be an unnecessary load for the drives.

Raid details (should they be relevant)

# mdadm --detail /dev/md3
/dev/md3:
        Version : 1.2
  Creation Time : Fri Aug  1 23:12:16 2014
     Raid Level : raid1
     Array Size : 1953381184 (1862.89 GiB 2000.26 GB)
  Used Dev Size : 1953381184 (1862.89 GiB 2000.26 GB)
   Raid Devices : 2
  Total Devices : 2
    Persistence : Superblock is persistent

    Update Time : Thu Sep 11 17:48:03 2014
          State : clean
 Active Devices : 2
Working Devices : 2
 Failed Devices : 0
  Spare Devices : 0

           Name : masysma-3:3  (local to host masysma-3)
           UUID : 5885863a:ca3648ff:7f73d47f:53f0476a
         Events : 75

    Number   Major   Minor   RaidDevice State
       2       8      129        0      active sync   /dev/sdi1
       1       8      145        1      active sync   /dev/sdj1

Also, this is the relevant line from mdadm.conf

ARRAY /dev/md/3 metadata=1.2 UUID=5885863a:ca3648ff:7f73d47f:53f0476a
name=masysma-3:3

TIA
Linux-Fan

--
http://masysma.lima-city.de/

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