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mdadm and raid0... will not reassemble.
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Joined: 09 Dec 2011
Posts: 51

PostPosted: Wed Sep 09, 2015 3:56 am    Post subject: mdadm and raid0... will not reassemble. Reply with quote

My first time messing around with raid, but it certainly seemed straight forward enough. I got a laptop with 3 hard drives and I want 2 of them in a raid0 for storage while the ssd carries Gentoo. sda and sdb are the raid array while sdc is the OS. Problem is that I have to recreate the array every reboot. The steps I took pre-file system were

mdadm --create /dev/md0 --level=0 --raid-devices=2 /dev/sda /dev/sdb

to create the array. I added the filesystem and mounted it to make sure everything worked and it did. So, I decided to do

mdadn --detail --scan -v >> /etc/mdadm.conf

to try and make it permanent. Well, upon reboot the array is assembled with no devices.

Before reboot mdadm --detail /dev/md0 produces

        Version : 1.2
  Creation Time : Tue Sep  8 18:59:18 2015
     Raid Level : raid0
     Array Size : 3906766848 (3725.78 GiB 4000.53 GB)
   Raid Devices : 2
  Total Devices : 2
    Persistence : Superblock is persistent

    Update Time : Tue Sep  8 18:59:18 2015
          State : clean
 Active Devices : 2
Working Devices : 2
 Failed Devices : 0
  Spare Devices : 0

     Chunk Size : 512K

           Name : purgatory:0  (local to host purgatory)
           UUID : 27c85d72:6eee5e74:69d0c1ea:cce19387
         Events : 0

    Number   Major   Minor   RaidDevice State
       0       8        0        0      active sync   /dev/sda
       1       8       16        1      active sync   /dev/sdb

After reboot:

Version: 0
Raid Level : raid0
Raid Devices : 0

Not sure what the problem is since my config file before reboot matches, but when I --stop md0 and then mdadm -A md0 it gives the same output until I mdadm --create again. My config file is as so: /etc/mdadm.conf

# mdadm configuration file
# mdadm will function properly without the use of a configuration file,
# but this file is useful for keeping track of arrays and member disks.
# In general, a mdadm.conf file is created, and updated, after arrays
# are created. This is the opposite behavior of /etc/raidtab which is
# created prior to array construction.
# the config file takes two types of lines:
#   DEVICE lines specify a list of devices of where to look for
#     potential member disks
#   ARRAY lines specify information about how to identify arrays so
#     so that they can be activated
# You can have more than one device line and use wild cards. The first
# example includes SCSI the first partition of SCSI disks /dev/sdb,
# /dev/sdc, /dev/sdd, /dev/sdj, /dev/sdk, and /dev/sdl. The second
# line looks for array slices on IDE disks.
#DEVICE partitions
#DEVICE /dev/hda1 /dev/hdb1
# If you mount devfs on /dev, then a suitable way to list all devices is:
#DEVICE /dev/discs/*/*
# The AUTO line can control which arrays get assembled by auto-assembly,
# meaing either "mdadm -As" when there are no 'ARRAY' lines in this file,
# or "mdadm --incremental" when the array found is not listed in this file.
# By default, all arrays that are found are assembled.
# If you want to ignore all DDF arrays (maybe they are managed by dmraid),
# and only assemble 1.x arrays if which are marked for 'this' homehost,
# but assemble all others, then use
#AUTO -ddf homehost -1.x +all
# ARRAY lines specify an array to assemble and a method of identification.
# Arrays can currently be identified by using a UUID, superblock minor number,
# or a listing of devices.
#   super-minor is usually the minor number of the metadevice
#   UUID is the Universally Unique Identifier for the array
# Each can be obtained using
#    mdadm -D <md>
#ARRAY /dev/md0 UUID=3aaa0122:29827cfa:5331ad66:ca767371
#ARRAY /dev/md1 super-minor=1
#ARRAY /dev/md2 devices=/dev/hda1,/dev/hdb1
# ARRAY lines can also specify a "spare-group" for each array.  mdadm --monitor
# will then move a spare between arrays in a spare-group if one array has a failed
# drive but no spare
#ARRAY /dev/md4 uuid=b23f3c6d:aec43a9f:fd65db85:369432df spare-group=group1
#ARRAY /dev/md5 uuid=19464854:03f71b1b:e0df2edd:246cc977 spare-group=group1
# When used in --follow (aka --monitor) mode, mdadm needs a
# mail address and/or a program.  This can be given with "mailaddr"
# and "program" lines to that monitoring can be started using
#    mdadm --follow --scan & echo $! > /run/mdadm/
# If the lines are not found, mdadm will exit quietly
#PROGRAM /usr/sbin/handle-mdadm-events

DEVICE partitions

ARRAY /dev/md0 level=raid0 num-devices=2 metadata=1.2 name=purgatory:0 UUID=38686c45:9b38fd8d:a8c6495a:c543d595 devices=/dev/sda,/dev/sdb

except that the uuid matches when I follow the step above. It's changed every time do --create again of course. Not sure where to go next since even mdadm -A /dev/md0 /dev/sda /dev/sdb tells me /dev/sda has no superblock:

mdadm -A /dev/md0 /dev/sda /dev/sdb
mdadm: Cannot assemble mbr metadata on /dev/sda
mdadm: /dev/sda has no superblock - assembly aborted

Therein, I have to --stop /dev/md0 and --create all over again and everything works fine except that I will eventually have to reboot again and create it again and can't mount it automagically. Any help is greatly appreciated. Thanks.
Autobots... roll out!!
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