Newly-created arrays don't auto-assemble - related to hostname change?

[Andy Smith <andy@strugglers.net>]

Hi,

I feel I am missing something very simple here, as I usually don't
have this issue, but here goes…

I've got a Debian jessie host on which I created four arrays during
install (md{0,1,2,3}), using the Debian installer and partman. These
auto-assemble fine.

After install the name of the server was changed from "tbd" to
"jfd". Another array was then created (md5), added to
/etc/mdadm/mdadm.conf and the initramfs was rebuilt
(update-initramfs -u).

md5 does not auto-assemble. It can be started fine after boot with:

    # mdadm --assemble /dev/md5

or:

    # mdadm --incremental /dev/sdc
    # mdadm --incremental /dev/sdd

/etc/mdadm/mdadm.conf:

    DEVICE /dev/sd*
    CREATE owner=root group=disk mode=0660 auto=yes
    HOMEHOST <ignore>
    MAILADDR root
    ARRAY /dev/md/0  metadata=1.2 UUID=400bac1d:e2c5d6ef:fea3b8c8:bcb70f8f
    ARRAY /dev/md/1  metadata=1.2 UUID=e29c8b89:705f0116:d888f77e:2b6e32f5
    ARRAY /dev/md/2  metadata=1.2 UUID=039b3427:4be5157a:6e2d53bd:fe898803
    ARRAY /dev/md/3  metadata=1.2 UUID=30f745ce:7ed41b53:4df72181:7406ea1d
    ARRAY /dev/md/5  metadata=1.2 UUID=957030cf:c09f023d:ceaebb27:e546f095

I've unpacked the initramfs and looked at the mdadm.conf in there
and it is identical.

Initially HOMEHOST was set to <system> (the default), but I noticed
when looking at --detail that md5 has:

           Name : jfd:5  (local to host jfd)

whereas the others have:

           Name : tbd:0

…so I changed it to <ignore> to see if that would help. It didn't.

So, I'd really appreciate any hints as to what I've missed here!

Here follows --detail and --examine of md5 and its members, then the
contents of /proc/mdstat after I have manually assembled md5.

$ sudo mdadm --detail /dev/md5
/dev/md5:
        Version : 1.2
  Creation Time : Thu Nov 17 02:35:15 2016
     Raid Level : raid10
     Array Size : 1875243008 (1788.37 GiB 1920.25 GB)
  Used Dev Size : 1875243008 (1788.37 GiB 1920.25 GB)
   Raid Devices : 2
  Total Devices : 2
    Persistence : Superblock is persistent

  Intent Bitmap : Internal

    Update Time : Thu Nov 17 02:35:15 2016
          State : clean 
 Active Devices : 2
Working Devices : 2
 Failed Devices : 0
  Spare Devices : 0

         Layout : far=2
     Chunk Size : 512K

           Name : jfd:5  (local to host jfd)
           UUID : 957030cf:c09f023d:ceaebb27:e546f095
         Events : 0

    Number   Major   Minor   RaidDevice State
       0       8       48        0      active sync   /dev/sdd
       1       8       32        1      active sync   /dev/sdc

$ sudo mdadm --examine /dev/sd{c,d}
/dev/sdc:
          Magic : a92b4efc
        Version : 1.2
    Feature Map : 0x1
     Array UUID : 957030cf:c09f023d:ceaebb27:e546f095
           Name : jfd:5  (local to host jfd)
  Creation Time : Thu Nov 17 02:35:15 2016
     Raid Level : raid10
   Raid Devices : 2

 Avail Dev Size : 3750486704 (1788.37 GiB 1920.25 GB)
     Array Size : 1875243008 (1788.37 GiB 1920.25 GB)
  Used Dev Size : 3750486016 (1788.37 GiB 1920.25 GB)
    Data Offset : 262144 sectors
   Super Offset : 8 sectors
   Unused Space : before=262056 sectors, after=688 sectors
          State : clean
    Device UUID : 4ac82c29:2d109465:7fff9b22:8c411c1e

Internal Bitmap : 8 sectors from superblock
    Update Time : Thu Nov 17 02:35:15 2016
  Bad Block Log : 512 entries available at offset 72 sectors
       Checksum : 96d669f1 - correct
         Events : 0

         Layout : far=2
     Chunk Size : 512K

   Device Role : Active device 1
   Array State : AA ('A' == active, '.' == missing, 'R' == replacing)
/dev/sdd:
          Magic : a92b4efc
        Version : 1.2
    Feature Map : 0x1
     Array UUID : 957030cf:c09f023d:ceaebb27:e546f095
           Name : jfd:5  (local to host jfd)
  Creation Time : Thu Nov 17 02:35:15 2016
     Raid Level : raid10
   Raid Devices : 2
 Avail Dev Size : 3750486704 (1788.37 GiB 1920.25 GB)
     Array Size : 1875243008 (1788.37 GiB 1920.25 GB)
  Used Dev Size : 3750486016 (1788.37 GiB 1920.25 GB)
    Data Offset : 262144 sectors
   Super Offset : 8 sectors
   Unused Space : before=262056 sectors, after=688 sectors
          State : clean
    Device UUID : 3a067652:6e88afae:82722342:0036bae0

Internal Bitmap : 8 sectors from superblock
    Update Time : Thu Nov 17 02:35:15 2016
  Bad Block Log : 512 entries available at offset 72 sectors
       Checksum : eb608799 - correct
         Events : 0

         Layout : far=2
     Chunk Size : 512K

   Device Role : Active device 0
   Array State : AA ('A' == active, '.' == missing, 'R' == replacing)

$ cat /proc/mdstat 
Personalities : [raid1] [raid10] 
md5 : active (auto-read-only) raid10 sdd[0] sdc[1]
      1875243008 blocks super 1.2 512K chunks 2 far-copies [2/2] [UU]
      bitmap: 0/14 pages [0KB], 65536KB chunk

md3 : active raid10 sda5[0] sdb5[1]
      12199936 blocks super 1.2 512K chunks 2 far-copies [2/2] [UU]
      
md2 : active (auto-read-only) raid10 sda3[0] sdb3[1]
      975872 blocks super 1.2 512K chunks 2 far-copies [2/2] [UU]
      
md1 : active raid10 sda2[0] sdb2[1]
      1951744 blocks super 1.2 512K chunks 2 far-copies [2/2] [UU]
      
md0 : active raid1 sda1[0] sdb1[1]
      498368 blocks super 1.2 [2/2] [UU]
      
unused devices: <none>

Cheers,
Andy