mdadm kernel log messages explained

mdadm kernel log messages explained

[Adam Ryczkowski]

Welcome.

(This email is a copy of serverfault question 
http://serverfault.com/questions/427692/mdadm-kernel-log-messages-explained, 
which I guess didn't get to the right audience)
I try to recover from linux software raid failure. I am in a process of 
recreating the superblocks based on a syslog from the system when it was 
healthy. The log speaks about 2 md devices, each based on 5 500GB 
partitions. The RAID-5 /dev/md5 is composed from /dev/sd[b-f]6 and 
RAID-6 /dev/md6 is composed from /dev/sd[b-f]5. The relevant part dmesg 
log is at bottom of this mail.

Questions:
#    What do the numbers on the line [ 5.979771] 4: w=1 pa=0 pr=5 m=1 
a=2 r=5 op1=0 op2=0 mean, including the first 4:?
#    What do the numbers on the line [ 6.039266] --- rd:5 wd:5] mean?
  #   What do the numbers on the line [ 6.046856] disk 0, o:1, dev:sdb6 
mean?
  #   Does the line [ 6.096768] created bitmap (15 pages) for device md5 
tell anything about the place, where the bitmap is located and what is 
its size?

|[    5.964928] raid5: allocated 5265kB for md5
[    5.979771] 4: w=1 pa=0 pr=5 m=1 a=2 r=5 op1=0 op2=0
[    5.987064] 1: w=2 pa=0 pr=5 m=1 a=2 r=5 op1=0 op2=0
[    5.994256] 3: w=3 pa=0 pr=5 m=1 a=2 r=5 op1=0 op2=0
[    6.001441] 2: w=4 pa=0 pr=5 m=1 a=2 r=5 op1=0 op2=0
[    6.008665] 0: w=5 pa=0 pr=5 m=1 a=2 r=5 op1=0 op2=0
[    6.015883] raid5: raid level 5 set md5 active with 5 out of 5 devices, algorithm 2
[    6.031441] RAID5 conf printout:
[    6.039266]  --- rd:5 wd:5
[    6.046856]  disk 0, o:1, dev:sdb6
[    6.054308]  disk 1, o:1, dev:sdf6
[    6.061524]  disk 2, o:1, dev:sdc6
[    6.068667]  disk 3, o:1, dev:sde6
[    6.075774]  disk 4, o:1, dev:sdd6
[    6.089504] md5: bitmap initialized from disk: read 1/1 pages, set 0 bits
[    6.096768] created bitmap (15 pages) for device md5
[    6.141010] md5: detected capacity change from 0 to 1978409418752
[    6.153794]  md5: unknown partition table

[    5.594614] raid5: device sde5 operational as raid disk 3
[    5.599701] raid5: device sdd5 operational as raid disk 4
[    5.604750] raid5: device sdf5 operational as raid disk 1
[    5.609879] raid5: device sdc5 operational as raid disk 2
[    5.615032] raid5: device sdb5 operational as raid disk 0
[    5.621672] raid5: allocated 5265kB for md6
[    5.627243] 3: w=1 pa=0 pr=5 m=2 a=2 r=5 op1=0 op2=0
[    5.632846] 4: w=2 pa=0 pr=5 m=2 a=2 r=5 op1=0 op2=0
[    5.638502] 1: w=3 pa=0 pr=5 m=2 a=2 r=5 op1=0 op2=0
[    5.644155] 2: w=4 pa=0 pr=5 m=2 a=2 r=5 op1=0 op2=0
[    5.649844] 0: w=5 pa=0 pr=5 m=2 a=2 r=5 op1=0 op2=0
[    5.655566] raid5: raid level 6 set md6 active with 5 out of 5 devices, algorithm 2
[    5.667653] RAID5 conf printout:
[    5.673791]  --- rd:5 wd:5
[    5.679837]  disk 0, o:1, dev:sdb5
[    5.685721]  disk 1, o:1, dev:sdf5
[    5.691570]  disk 2, o:1, dev:sdc5
[    5.697348]  disk 3, o:1, dev:sde5
[    5.703122]  disk 4, o:1, dev:sdd5
[    5.710762] md6: bitmap initialized from disk: read 1/1 pages, set 0 bits
[    5.716915] created bitmap (15 pages) for device md6|

-- 
Adam Ryczkowski
Skype:sisteczko

mdadm kernel log messages explained

[Adam Ryczkowski]

Welcome.

I try to recover from linux software raid failure. I am in a process of 
recreating the superblocks based on a syslog from the system when it was 
healthy. The log speaks about 2 md devices, each based on 5 500GB 
partitions. The RAID-5 /dev/md5 is composed from /dev/sd[b-f]6 and 
RAID-6 /dev/md6 is composed from /dev/sd[b-f]5. The relevant part dmesg 
log looks like this:

Questions:
#    What do the numbers on the line [ 5.979771] 4: w=1 pa=0 pr=5 m=1 
a=2 r=5 op1=0 op2=0 mean, including the first 4:?
#    What do the numbers on the line [ 6.039266] --- rd:5 wd:5] mean?
#    What do the numbers on the line [ 6.046856] disk 0, o:1, dev:sdb6 mean?
#    Does the line [ 6.096768] created bitmap (15 pages) for device md5 
tell anything about the place, where the bitmap is located and what is 
its size?

The messages are produced by the 2.6.32 kernel, Ubuntu Lucid.

(This mail is a copy of serverfault question 
(http://serverfault.com/questions/427692/mdadm-kernel-log-messages-explained) 
which I guess didn't get to the right audience)

[    5.964928] raid5: allocated 5265kB for md5
[    5.979771] 4: w=1 pa=0 pr=5 m=1 a=2 r=5 op1=0 op2=0
[    5.987064] 1: w=2 pa=0 pr=5 m=1 a=2 r=5 op1=0 op2=0
[    5.994256] 3: w=3 pa=0 pr=5 m=1 a=2 r=5 op1=0 op2=0
[    6.001441] 2: w=4 pa=0 pr=5 m=1 a=2 r=5 op1=0 op2=0
[    6.008665] 0: w=5 pa=0 pr=5 m=1 a=2 r=5 op1=0 op2=0
[    6.015883] raid5: raid level 5 set md5 active with 5 out of 5 
devices, algorithm 2
[    6.031441] RAID5 conf printout:
[    6.039266]  --- rd:5 wd:5
[    6.046856]  disk 0, o:1, dev:sdb6
[    6.054308]  disk 1, o:1, dev:sdf6
[    6.061524]  disk 2, o:1, dev:sdc6
[    6.068667]  disk 3, o:1, dev:sde6
[    6.075774]  disk 4, o:1, dev:sdd6
[    6.089504] md5: bitmap initialized from disk: read 1/1 pages, set 0 bits
[    6.096768] created bitmap (15 pages) for device md5
[    6.141010] md5: detected capacity change from 0 to 1978409418752
[    6.153794]  md5: unknown partition table

[    5.594614] raid5: device sde5 operational as raid disk 3
[    5.599701] raid5: device sdd5 operational as raid disk 4
[    5.604750] raid5: device sdf5 operational as raid disk 1
[    5.609879] raid5: device sdc5 operational as raid disk 2
[    5.615032] raid5: device sdb5 operational as raid disk 0
[    5.621672] raid5: allocated 5265kB for md6
[    5.627243] 3: w=1 pa=0 pr=5 m=2 a=2 r=5 op1=0 op2=0
[    5.632846] 4: w=2 pa=0 pr=5 m=2 a=2 r=5 op1=0 op2=0
[    5.638502] 1: w=3 pa=0 pr=5 m=2 a=2 r=5 op1=0 op2=0
[    5.644155] 2: w=4 pa=0 pr=5 m=2 a=2 r=5 op1=0 op2=0
[    5.649844] 0: w=5 pa=0 pr=5 m=2 a=2 r=5 op1=0 op2=0
[    5.655566] raid5: raid level 6 set md6 active with 5 out of 5 
devices, algorithm 2
[    5.667653] RAID5 conf printout:
[    5.673791]  --- rd:5 wd:5
[    5.679837]  disk 0, o:1, dev:sdb5
[    5.685721]  disk 1, o:1, dev:sdf5
[    5.691570]  disk 2, o:1, dev:sdc5
[    5.697348]  disk 3, o:1, dev:sde5
[    5.703122]  disk 4, o:1, dev:sdd5
[    5.710762] md6: bitmap initialized from disk: read 1/1 pages, set 0 bits
[    5.716915] created bitmap (15 pages) for device md6



-- 
Adam Ryczkowski
Skype:sisteczko

Re: mdadm kernel log messages explained

[Robin Hill]

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On Sun Sep 16, 2012 at 11:01:41 +0200, Adam Ryczkowski wrote:

> Welcome.
> 
> I try to recover from linux software raid failure. I am in a process of 
> recreating the superblocks based on a syslog from the system when it was 
> healthy. The log speaks about 2 md devices, each based on 5 500GB 
> partitions. The RAID-5 /dev/md5 is composed from /dev/sd[b-f]6 and 
> RAID-6 /dev/md6 is composed from /dev/sd[b-f]5. The relevant part dmesg 
> log looks like this:
> 
> Questions:
> #    What do the numbers on the line [ 5.979771] 4: w=1 pa=0 pr=5 m=1 
> a=2 r=5 op1=0 op2=0 mean, including the first 4:?
4 is the raid device number
w=1 indicates the number of working disks found so far
pa=0 is the previous algorithm (used when reshaping)
pr=5 is the previous number of raid devices (used when reshaping)
m=1 is the maximum number of degraded disks allowed for the array to run
a=2 is the algorithm used
r=5 is the number of raid devices
op1=0 indicates that the disk is not a parity-only disk in the previous
      layout (used when reshaping)
op2=0 indicates that the disk is not a parity-only disk in the current
      layout

> #    What do the numbers on the line [ 6.039266] --- rd:5 wd:5] mean?
rd is the number of devices in the array
wd is the number of working devices in the array

> #    What do the numbers on the line [ 6.046856] disk 0, o:1, dev:sdb6 mean?
0 is the raid device number
o:1 indicates that it's operational (i.e. not marked as faulty)
dev:sdb6 indicates the kernel device name

> #    Does the line [ 6.096768] created bitmap (15 pages) for device md5 
> tell anything about the place, where the bitmap is located and what is 
> its size?
> 
It doesn't tell you anything about the place. I've no idea how the
number of pages equates to the bitmap size/bitmap chunk size though.

In the above cases, the raid device number is its position within the
array, so from 0..N-1 for an N-device array. This will indicate the
order you'll need to use when recreating the array.

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

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