How best to re-sync raid1 array? zero superblock on removed disk and let it rebuild?

How best to re-sync raid1 array? zero superblock on removed disk and let it rebuild?

[David C. Rankin]

All,

   I had a disc-controller failure on a server running several raid1 arrays. The 
disks are fine, but I have had the root partition come up in degraded mode. What 
is the best way to tell mdraid to resync the disks? Here are the symptoms:

# cat /proc/mdstat
Personalities : [raid1]
md1 : active raid1 sdb7[1]
       52396032 blocks super 1.2 [2/1] [_U]

md3 : active raid1 sdb6[1] sda6[0]
       1047552 blocks super 1.2 [2/2] [UU]

md2 : active raid1 sda8[0] sdb8[1]
       922944192 blocks super 1.2 [2/2] [UU]
       bitmap: 0/7 pages [0KB], 65536KB chunk

md0 : active raid1 sda5[0] sdb5[1]
       204608 blocks super 1.2 [2/2] [UU]

unused devices: <none>

# mdadm --misc --detail /dev/md1
/dev/md1:
         Version : 1.2
   Creation Time : Wed Nov 27 04:35:49 2013
      Raid Level : raid1
      Array Size : 52396032 (49.97 GiB 53.65 GB)
   Used Dev Size : 52396032 (49.97 GiB 53.65 GB)
    Raid Devices : 2
   Total Devices : 1
     Persistence : Superblock is persistent

     Update Time : Fri Aug 28 04:12:18 2015
           State : clean, degraded
  Active Devices : 1
Working Devices : 1
  Failed Devices : 0
   Spare Devices : 0

            Name : archiso:1
            UUID : 320d86f7:22999af5:5eeefee1:35cd8970
          Events : 100308

     Number   Major   Minor   RaidDevice State
        0       0        0        0      removed
        1       8       23        1      active sync   /dev/sdb7

Reading, it looks like one approach is the boot the install media and then zero 
the superblock on /dev/sda7 and then reboot. Will that force a rebuild, or do I 
need to fail and remove the disk first? I was thinking:

# mdadm --zero-superblock /dev/sda7

should set it up for a rebuild without more. Is this a sane approach?

-- 
David C. Rankin, J.D.,P.E.

Re: How best to re-sync raid1 array? zero superblock on removed disk and let it rebuild?

[David C. Rankin]

On 08/28/2015 04:22 AM, David C. Rankin wrote:
> All,
>
>    I had a disc-controller failure on a server running several raid1 arrays. The
> disks are fine, but I have had the root partition come up in degraded mode. What
> is the best way to tell mdraid to resync the disks? Here are the symptoms:
>
> # cat /proc/mdstat
> Personalities : [raid1]
> md1 : active raid1 sdb7[1]
>        52396032 blocks super 1.2 [2/1] [_U]
>
> md3 : active raid1 sdb6[1] sda6[0]
>        1047552 blocks super 1.2 [2/2] [UU]
>
> md2 : active raid1 sda8[0] sdb8[1]
>        922944192 blocks super 1.2 [2/2] [UU]
>        bitmap: 0/7 pages [0KB], 65536KB chunk
>
> md0 : active raid1 sda5[0] sdb5[1]
>        204608 blocks super 1.2 [2/2] [UU]
>
> unused devices: <none>
>
> # mdadm --misc --detail /dev/md1
> /dev/md1:
>          Version : 1.2
>    Creation Time : Wed Nov 27 04:35:49 2013
>       Raid Level : raid1
>       Array Size : 52396032 (49.97 GiB 53.65 GB)
>    Used Dev Size : 52396032 (49.97 GiB 53.65 GB)
>     Raid Devices : 2
>    Total Devices : 1
>      Persistence : Superblock is persistent
>
>      Update Time : Fri Aug 28 04:12:18 2015
>            State : clean, degraded
>   Active Devices : 1
> Working Devices : 1
>   Failed Devices : 0
>    Spare Devices : 0
>
>             Name : archiso:1
>             UUID : 320d86f7:22999af5:5eeefee1:35cd8970
>           Events : 100308
>
>      Number   Major   Minor   RaidDevice State
>         0       0        0        0      removed
>         1       8       23        1      active sync   /dev/sdb7
>
> Reading, it looks like one approach is the boot the install media and then zero
> the superblock on /dev/sda7 and then reboot. Will that force a rebuild, or do I
> need to fail and remove the disk first? I was thinking:
>
> # mdadm --zero-superblock /dev/sda7
>
> should set it up for a rebuild without more. Is this a sane approach?
>

This adds a bit more of the picture. It's like sda7 doesn't even know it was 
kicked out. There are no disk errors logged for either of the drives:

  # mdadm -E /dev/sd[ab]7
/dev/sda7:
           Magic : a92b4efc
         Version : 1.2
     Feature Map : 0x8
      Array UUID : 320d86f7:22999af5:5eeefee1:35cd8970
            Name : archiso:1
   Creation Time : Wed Nov 27 04:35:49 2013
      Raid Level : raid1
    Raid Devices : 2

  Avail Dev Size : 104792064 (49.97 GiB 53.65 GB)
      Array Size : 52396032 (49.97 GiB 53.65 GB)
     Data Offset : 65536 sectors
    Super Offset : 8 sectors
    Unused Space : before=65448 sectors, after=0 sectors
           State : active
     Device UUID : f5a48ea1:bce2f6f0:f47f9c0b:bad1d64d

     Update Time : Sat Aug  8 17:17:21 2015
   Bad Block Log : 512 entries available at offset 72 sectors - bad blocks present.
        Checksum : 2c45bcef - correct
          Events : 280


    Device Role : Active device 0
    Array State : AA ('A' == active, '.' == missing, 'R' == replacing)
/dev/sdb7:
           Magic : a92b4efc
         Version : 1.2
     Feature Map : 0x8
      Array UUID : 320d86f7:22999af5:5eeefee1:35cd8970
            Name : archiso:1
   Creation Time : Wed Nov 27 04:35:49 2013
      Raid Level : raid1
    Raid Devices : 2

  Avail Dev Size : 104792064 (49.97 GiB 53.65 GB)
      Array Size : 52396032 (49.97 GiB 53.65 GB)
     Data Offset : 65536 sectors
    Super Offset : 8 sectors
    Unused Space : before=65448 sectors, after=0 sectors
           State : clean
     Device UUID : 66e069cc:02daa93e:1d4a6eea:e5c21cb7

     Update Time : Fri Aug 28 04:35:31 2015
   Bad Block Log : 512 entries available at offset 72 sectors - bad blocks present.
        Checksum : ed07de3b - correct
          Events : 100584


    Device Role : Active device 1
    Array State : .A ('A' == active, '.' == missing, 'R' == replacing)

Do I try a --re-add on sda7 or just zero it for a complete rebuild? Any help 
appreciated.

-- 
David C. Rankin, J.D.,P.E.

Re: How best to re-sync raid1 array? zero superblock on removed disk and let it rebuild?

[Robin Hill]

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On Fri Aug 28, 2015 at 04:22:09am -0500, David C. Rankin wrote:

> All,
> 
>    I had a disc-controller failure on a server running several raid1
> arrays. The disks are fine, but I have had the root partition come up
> in degraded mode. What is the best way to tell mdraid to resync the
> disks? Here are the symptoms:
> 
> # cat /proc/mdstat
> Personalities : [raid1]
> md1 : active raid1 sdb7[1]
>        52396032 blocks super 1.2 [2/1] [_U]
> 
> md3 : active raid1 sdb6[1] sda6[0]
>        1047552 blocks super 1.2 [2/2] [UU]
> 
> md2 : active raid1 sda8[0] sdb8[1]
>        922944192 blocks super 1.2 [2/2] [UU]
>        bitmap: 0/7 pages [0KB], 65536KB chunk
> 
> md0 : active raid1 sda5[0] sdb5[1]
>        204608 blocks super 1.2 [2/2] [UU]
> 
> unused devices: <none>
> 
<- snip ->
> Reading, it looks like one approach is the boot the install media and
> then zero the superblock on /dev/sda7 and then reboot. Will that force
> a rebuild, or do I need to fail and remove the disk first? I was thinking:
> 
> # mdadm --zero-superblock /dev/sda7
> 
> should set it up for a rebuild without more. Is this a sane approach?
> 
No need to over-complicate things. The only issue you have looks to be
that sda7 has not come up as part of md1, so just add it back in:
    mdadm /dev/md1 -a /dev/sda7

You probably want to check dmesg, etc. to see why it didn't get added in
at all in the first place (I'd have expected it to be at least in as a
spare).

Cheers,
    Robin
-- 
     ___        
    ( ' }     |       Robin Hill        <robin@robinhill.me.uk> |
   / / )      | Little Jim says ....                            |
  // !!       |      "He fallen in de water !!"                 |

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Re: How best to re-sync raid1 array? zero superblock on removed disk and let it rebuild?

[Mikael Abrahamsson]

On Fri, 28 Aug 2015, David C. Rankin wrote:

> Do I try a --re-add on sda7 or just zero it for a complete rebuild? Any 
> help appreciated.

Since sda7 has a much lower event count, it doesn't really matter. You do 
not have a bitmap enabled and so since the event counts are off, a 
complete resync will need to happen either way.

If --re-add doesn't work, use --add. If that doesn't work, zero superblock 
and --add.

-- 
Mikael Abrahamsson    email: swmike@swm.pp.se

Re: How best to re-sync raid1 array? zero superblock on removed disk and let it rebuild?

[David C. Rankin]

On 08/28/2015 04:52 AM, Robin Hill wrote:
> On Fri Aug 28, 2015 at 04:22:09am -0500, David C. Rankin wrote:
>
>> Reading, it looks like one approach is the boot the install media and
>> then zero the superblock on /dev/sda7 and then reboot. Will that force
>> a rebuild, or do I need to fail and remove the disk first? I was thinking:
>>
>> # mdadm --zero-superblock /dev/sda7
>>
>> should set it up for a rebuild without more. Is this a sane approach?
>>
> No need to over-complicate things. The only issue you have looks to be
> that sda7 has not come up as part of md1, so just add it back in:
>      mdadm /dev/md1 -a /dev/sda7
>
> You probably want to check dmesg, etc. to see why it didn't get added in
> at all in the first place (I'd have expected it to be at least in as a
> spare).
>
> Cheers,
>      Robin
>

Hah!

   You guys are great!

[07:57 phoinix:.../david/dev] #  mdadm /dev/md1 -a /dev/sda7
mdadm: added /dev/sda7
[07:58 phoinix:.../david/dev] # cat /proc/mdstat
Personalities : [raid1]
md1 : active raid1 sda7[2] sdb7[1]
       52396032 blocks super 1.2 [2/1] [_U]
       [=>...................]  recovery =  6.1% (3246848/52396032) 
finish=9.7min speed=83527K/sec

   I have no clue what happened? I have never seen this before. There was never 
an attempt to md: bind<sda7> (just like it didn't exist). The only thing 
different about this boot (aside from the new highpoint raid controller) was the 
fact I left the Arch install CD in the CD/DVD drive. I don't know if in the 
early boot process, prior to the handoff to the highpoint controller, it somehow 
may have grabbed sda?? (the CD drive is still on the onboard ATA controller, 
while all SATA drives are attached to the highpoint controller).

   Let me know if you see anything that makes any more sense?

   And... during the time it took to compose this reply:

Personalities : [raid1]
md1 : active raid1 sda7[2] sdb7[1]
       52396032 blocks super 1.2 [2/2] [UU]

md3 : active raid1 sdb6[1] sda6[0]
       1047552 blocks super 1.2 [2/2] [UU]

md2 : active raid1 sda8[0] sdb8[1]
       922944192 blocks super 1.2 [2/2] [UU]
       bitmap: 0/7 pages [0KB], 65536KB chunk

md0 : active raid1 sda5[0] sdb5[1]
       204608 blocks super 1.2 [2/2] [UU]

unused devices: <none>

   Whoop!

   I've gathered the relevant dmesg output. Maybe you can help make sense out of 
it. It just looks like the system never tried to activate sda7...

[    3.261932] sd 3:0:0:0: [sdb] 1953525168 512-byte logical blocks: (1.00 
TB/931 GiB)
[    3.261948] sd 2:0:0:0: [sda] 1953525168 512-byte logical blocks: (1.00 
TB/931 GiB)
[    3.261988] sd 2:0:0:0: [sda] Write Protect is off
[    3.261990] sd 2:0:0:0: [sda] Mode Sense: 00 3a 00 00
[    3.262010] sd 3:0:0:0: [sdb] Write Protect is off
[    3.262012] sd 2:0:0:0: [sda] Write cache: enabled, read cache: enabled, 
doesn't support DPO or FUA
[    3.262018] sd 3:0:0:0: [sdb] Mode Sense: 00 3a 00 00
[    3.262034] sd 3:0:0:0: [sdb] Write cache: enabled, read cache: enabled, 
doesn't support DPO or FUA
[    3.298037]  sda: sda1 < sda5 sda6 sda7 sda8 >
[    3.298469] sd 2:0:0:0: [sda] Attached SCSI disk
[    3.317052]  sdb: sdb1 < sdb5 sdb6 sdb7 sdb8 >
[    3.317456] sd 3:0:0:0: [sdb] Attached SCSI disk
[    3.420533] md: bind<sdb5>
[    3.421641] md: bind<sdb8>
[    3.423385] md: bind<sda8>
[    3.425987] md: raid1 personality registered for level 1
[    3.426035] md: bind<sda5>
[    3.426204] md/raid1:md2: active with 2 out of 2 mirrors
[    3.426322] created bitmap (7 pages) for device md2
[    3.426614] md2: bitmap initialized from disk: read 1 pages, set 0 of 14084 bits
[    3.427474] md/raid1:md0: active with 2 out of 2 mirrors
[    3.427496] md0: detected capacity change from 0 to 209518592
[    3.469789]  md0: unknown partition table
[    3.543932] md2: detected capacity change from 0 to 945094852608
[    3.544373] md: bind<sda6>
[    3.545918] md: bind<sdb6>
[    3.546646]  md2: unknown partition table
[    3.547402] md/raid1:md3: active with 2 out of 2 mirrors
[    3.547428] md3: detected capacity change from 0 to 1072693248
[    3.547986] md: bind<sdb7>
[    3.549323] md/raid1:md1: active with 1 out of 2 mirrors
[    3.549348] md1: detected capacity change from 0 to 53653536768
[    3.558920]  md3: unknown partition table
[    3.559052]  md1: unknown partition table
[    4.345217]  md1: unknown partition table
[    4.371798] EXT4-fs (md1): mounted filesystem with ordered data mode. Opts: 
(null)
<snip>
[    6.020249] EXT4-fs (md1): re-mounted. Opts: stripe=32,data=ordered
[    6.020965] systemd[1]: Started Remount Root and Kernel File Systems.
<snip>
[   10.110516]  md0: unknown partition table
[   10.480935]  md2: unknown partition table
[   10.531124] EXT4-fs (md0): mounted filesystem with ordered data mode. Opts: 
stripe=32,data=ordered
[   10.573132] EXT4-fs (md2): mounted filesystem with ordered data mode. Opts: 
stripe=32,data=ordered
<snip>
[223796.599863] md: export_rdev(sda7)
[223796.658203] md: bind<sda7>
[223796.719104]  disk 0, wo:1, o:1, dev:sda7
[223796.719108]  disk 1, wo:0, o:1, dev:sdb7
[223796.719155] md: recovery of RAID array md1
[223796.719156] md: minimum _guaranteed_  speed: 1000 KB/sec/disk.
[223796.719158] md: using maximum available idle IO bandwidth (but not more than 
200000 KB/sec) for recovery.
[223796.719161] md: using 128k window, over a total of 52396032k.


-- 
David C. Rankin, J.D.,P.E.