Hi guys,
I'm new to RAID although I've had a server running raid5 for a while.
It was delivered preinstalled like this and I never really wondered
how to monitor and maintain it. This quick introduction just to let
you understand why I'm such an idiot asking such a silly question.
Now what happened?
I have a server with 4 disks and raid5 configured. /dev/md10 is made
of sda10 , sdb10 , sdc10 and sdd10 .
Unfortunately, /dev/sdd died, the server crashed, etc. After restart,
md10 did not rebuilt. I understood sdd was dead and did not try to
force rebuild or even touch the existing system.
First thing I did is ddrescue the remaining partitions sd[abc]10 .
ddrescue did not stumble into any read error so I assume all remaining
partitions are perfectly safe.
Then I examined the partitions with :
================================================================================
# mdadm --examine /dev/loop[012]
/dev/loop0:
Magic : a92b4efc
Version : 0.90.00
UUID : 9d37bc89:711887ae:a4d2adc2:26fd5302
Creation Time : Wed Jan 25 09:08:11 2012
Raid Level : raid5
Used Dev Size : 1926247296 (1837.01 GiB 1972.48 GB)
Array Size : 5778741888 (5511.04 GiB 5917.43 GB)
Raid Devices : 4
Total Devices : 4
Preferred Minor : 10
Update Time : Mon Sep 5 23:29:23 2016
State : clean
Active Devices : 3
Working Devices : 3
Failed Devices : 1
Spare Devices : 0
Checksum : 9d0ce26d - correct
Events : 81589
Layout : left-symmetric
Chunk Size : 64K
Number Major Minor RaidDevice State
this 0 8 10 0 active sync
0 0 8 10 0 active sync
1 1 8 26 1 active sync
2 2 8 42 2 active sync
3 3 0 0 3 faulty removed
/dev/loop1:
Magic : a92b4efc
Version : 0.90.00
UUID : 9d37bc89:711887ae:a4d2adc2:26fd5302
Creation Time : Wed Jan 25 09:08:11 2012
Raid Level : raid5
Used Dev Size : 1926247296 (1837.01 GiB 1972.48 GB)
Array Size : 5778741888 (5511.04 GiB 5917.43 GB)
Raid Devices : 4
Total Devices : 4
Preferred Minor : 10
Update Time : Mon Sep 5 23:36:23 2016
State : clean
Active Devices : 1
Working Devices : 1
Failed Devices : 2
Spare Devices : 0
Checksum : 9d0ce487 - correct
Events : 81626
Layout : left-symmetric
Chunk Size : 64K
Number Major Minor RaidDevice State
this 1 8 26 1 active sync
0 0 0 0 0 removed
1 1 8 26 1 active sync
2 2 0 0 2 faulty removed
3 3 0 0 3 faulty removed
/dev/loop2:
Magic : a92b4efc
Version : 0.90.00
UUID : 9d37bc89:711887ae:a4d2adc2:26fd5302
Creation Time : Wed Jan 25 09:08:11 2012
Raid Level : raid5
Used Dev Size : 1926247296 (1837.01 GiB 1972.48 GB)
Array Size : 5778741888 (5511.04 GiB 5917.43 GB)
Raid Devices : 4
Total Devices : 4
Preferred Minor : 10
Update Time : Mon Sep 5 23:29:23 2016
State : clean
Active Devices : 3
Working Devices : 3
Failed Devices : 1
Spare Devices : 0
Checksum : 9d0ce291 - correct
Events : 81589
Layout : left-symmetric
Chunk Size : 64K
Number Major Minor RaidDevice State
this 2 8 42 2 active sync
0 0 8 10 0 active sync
1 1 8 26 1 active sync
2 2 8 42 2 active sync
3 3 0 0 3 faulty removed
================================================================================
There comes my mistake: I ran the --create command instead of --assemble :
================================================================================
# mdadm --create --verbose /dev/md1 --raid-devices=4 --level=raid5
--run --readonly /dev/loop0 /dev/loop1 /dev/loop2 missing
mdadm: layout defaults to left-symmetric
mdadm: layout defaults to left-symmetric
mdadm: chunk size defaults to 512K
mdadm: /dev/loop0 appears to contain an ext2fs file system
size=5778741888K mtime=Sat Sep 3 11:00:22 2016
mdadm: /dev/loop0 appears to be part of a raid array:
level=raid5 devices=4 ctime=Wed Jan 25 09:08:11 2012
mdadm: /dev/loop1 appears to be part of a raid array:
level=raid5 devices=4 ctime=Wed Jan 25 09:08:11 2012
mdadm: /dev/loop2 appears to be part of a raid array:
level=raid5 devices=4 ctime=Wed Jan 25 09:08:11 2012
mdadm: size set to 1926115840K
mdadm: automatically enabling write-intent bitmap on large array
mdadm: creation continuing despite oddities due to --run
mdadm: Defaulting to version 1.2 metadata
mdadm: array /dev/md1 started.
================================================================================
After that, mounting failed:
================================================================================
# mount /dev/md1 /raid/
mount: /dev/md1 is write-protected, mounting read-only
mount: wrong fs type, bad option, bad superblock on /dev/md1,
missing codepage or helper program, or other error
In some cases useful info is found in syslog - try
dmesg | tail or so.
================================================================================
Here's more info about the new raid to be compared with the initial one:
================================================================================
# mdadm --examine /dev/loop[012]
/dev/loop0:
Magic : a92b4efc
Version : 1.2
Feature Map : 0x1
Array UUID : aa56f42f:bb95fbde:11ce620e:878b2b1c
Name : tucana.caoba.fr:1 (local to host tucana.caoba.fr)
Creation Time : Mon Sep 19 23:17:04 2016
Raid Level : raid5
Raid Devices : 4
Avail Dev Size : 3852232703 (1836.89 GiB 1972.34 GB)
Array Size : 5778347520 (5510.66 GiB 5917.03 GB)
Used Dev Size : 3852231680 (1836.89 GiB 1972.34 GB)
Data Offset : 262144 sectors
Super Offset : 8 sectors
Unused Space : before=262056 sectors, after=1023 sectors
State : clean
Device UUID : b4622e59:f0735f5a:825086d1:57f89efb
Internal Bitmap : 8 sectors from superblock
Update Time : Mon Sep 19 23:17:04 2016
Bad Block Log : 512 entries available at offset 72 sectors
Checksum : 3ec8dda7 - correct
Events : 0
Layout : left-symmetric
Chunk Size : 512K
Device Role : Active device 0
Array State : AAA. ('A' == active, '.' == missing, 'R' == replacing)
/dev/loop1:
Magic : a92b4efc
Version : 1.2
Feature Map : 0x1
Array UUID : aa56f42f:bb95fbde:11ce620e:878b2b1c
Name : tucana.caoba.fr:1 (local to host tucana.caoba.fr)
Creation Time : Mon Sep 19 23:17:04 2016
Raid Level : raid5
Raid Devices : 4
Avail Dev Size : 3852232703 (1836.89 GiB 1972.34 GB)
Array Size : 5778347520 (5510.66 GiB 5917.03 GB)
Used Dev Size : 3852231680 (1836.89 GiB 1972.34 GB)
Data Offset : 262144 sectors
Super Offset : 8 sectors
Unused Space : before=262056 sectors, after=1023 sectors
State : clean
Device UUID : 9d42153b:4173aeea:51f41ebc:3789f98a
Internal Bitmap : 8 sectors from superblock
Update Time : Mon Sep 19 23:17:04 2016
Bad Block Log : 512 entries available at offset 72 sectors
Checksum : 2af1f191 - correct
Events : 0
Layout : left-symmetric
Chunk Size : 512K
Device Role : Active device 1
Array State : AAA. ('A' == active, '.' == missing, 'R' == replacing)
/dev/loop2:
Magic : a92b4efc
Version : 1.2
Feature Map : 0x1
Array UUID : aa56f42f:bb95fbde:11ce620e:878b2b1c
Name : tucana.caoba.fr:1 (local to host tucana.caoba.fr)
Creation Time : Mon Sep 19 23:17:04 2016
Raid Level : raid5
Raid Devices : 4
Avail Dev Size : 3852232703 (1836.89 GiB 1972.34 GB)
Array Size : 5778347520 (5510.66 GiB 5917.03 GB)
Used Dev Size : 3852231680 (1836.89 GiB 1972.34 GB)
Data Offset : 262144 sectors
Super Offset : 8 sectors
Unused Space : before=262056 sectors, after=1023 sectors
State : clean
Device UUID : ada52b0e:f2c4a680:ece59800:6425a9b2
Internal Bitmap : 8 sectors from superblock
Update Time : Mon Sep 19 23:17:04 2016
Bad Block Log : 512 entries available at offset 72 sectors
Checksum : 2a341a - correct
Events : 0
Layout : left-symmetric
Chunk Size : 512K
Device Role : Active device 2
Array State : AAA. ('A' == active, '.' == missing, 'R' == replacing)
================================================================================
With the help of the initial mdadm --examine , is it possible to
recreate my raid in a way that I can read data out of it?
I also posted the question here:
http://www.unix.com/unix-for-advanced-and-expert-users/268771-how-fix-mistake-raid-mdadm-create-instead-assemble-post302983179.html#post302983179
Regards
-------------------------
Santiago DIEZ
CAOBA Conseil
Paris, France
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