(help!) MD RAID6 won't --re-add devices?

(help!) MD RAID6 won't --re-add devices?

[Bart Kus]

Hello,

I had a Port Multiplier failure overnight.  This put 5 out of 10 drives 
offline, degrading my RAID6 array.  The file system is still mounted 
(and failing to write):

Buffer I/O error on device md4, logical block 3907023608
Filesystem "md4": xfs_log_force: error 5 returned.
etc...

The array is in the following state:

/dev/md4:
         Version : 1.02
   Creation Time : Sun Aug 10 23:41:49 2008
      Raid Level : raid6
      Array Size : 15628094464 (14904.11 GiB 16003.17 GB)
   Used Dev Size : 1953511808 (1863.01 GiB 2000.40 GB)
    Raid Devices : 10
   Total Devices : 11
     Persistence : Superblock is persistent

     Update Time : Wed Jan 12 05:32:14 2011
           State : clean, degraded
  Active Devices : 5
Working Devices : 5
  Failed Devices : 6
   Spare Devices : 0

      Chunk Size : 64K

            Name : 4
            UUID : da14eb85:00658f24:80f7a070:b9026515
          Events : 4300692

     Number   Major   Minor   RaidDevice State
       15       8        1        0      active sync   /dev/sda1
        1       0        0        1      removed
       12       8       33        2      active sync   /dev/sdc1
       16       8       49        3      active sync   /dev/sdd1
        4       0        0        4      removed
       20       8      193        5      active sync   /dev/sdm1
        6       0        0        6      removed
        7       0        0        7      removed
        8       0        0        8      removed
       13       8       17        9      active sync   /dev/sdb1

       10       8       97        -      faulty spare
       11       8      129        -      faulty spare
       14       8      113        -      faulty spare
       17       8       81        -      faulty spare
       18       8       65        -      faulty spare
       19       8      145        -      faulty spare

I have replaced the faulty PM and the drives have registered back with 
the system, under new names:

sd 3:0:0:0: [sdn] Attached SCSI disk
sd 3:1:0:0: [sdo] Attached SCSI disk
sd 3:2:0:0: [sdp] Attached SCSI disk
sd 3:4:0:0: [sdr] Attached SCSI disk
sd 3:3:0:0: [sdq] Attached SCSI disk

But I can't seem to --re-add them into the array now!

# mdadm /dev/md4 --re-add /dev/sdn1 --re-add /dev/sdo1 --re-add 
/dev/sdp1 --re-add /dev/sdr1 --re-add /dev/sdq1
mdadm: add new device failed for /dev/sdn1 as 21: Device or resource busy

I haven't unmounted the file system and/or stopped the /dev/md4 device, 
since I think that would drop any buffers either layer might be 
holding.  I'd of course prefer to lose as little data as possible.  How 
can I get this array going again?

PS: I think the reason "Failed Devices" shows 6 and not 5 is because I 
had a single HD failure a couple weeks back.  I replaced the drive and 
the array re-built A-OK.  I guess it still counted the failure since the 
array wasn't stopped during the repair.

Thanks for any guidance,

--Bart

PPS: mdadm - v3.0 - 2nd June 2009
PPS: Linux jo.bartk.us 2.6.35-gentoo-r9 #1 SMP Sat Oct 2 21:22:14 PDT 
2010 x86_64 Intel(R) Core(TM)2 Quad CPU @ 2.40GHz GenuineIntel GNU/Linux
PPS:  # mdadm --examine /dev/sdn1
/dev/sdn1:
           Magic : a92b4efc
         Version : 1.2
     Feature Map : 0x0
      Array UUID : da14eb85:00658f24:80f7a070:b9026515
            Name : 4
   Creation Time : Sun Aug 10 23:41:49 2008
      Raid Level : raid6
    Raid Devices : 10

  Avail Dev Size : 3907023730 (1863.01 GiB 2000.40 GB)
      Array Size : 31256188928 (14904.11 GiB 16003.17 GB)
   Used Dev Size : 3907023616 (1863.01 GiB 2000.40 GB)
     Data Offset : 272 sectors
    Super Offset : 8 sectors
           State : clean
     Device UUID : c0cf419f:4c33dc64:84bc1c1a:7e9778ba

     Update Time : Wed Jan 12 05:39:55 2011
        Checksum : bdb14e66 - correct
          Events : 4300672

      Chunk Size : 64K

    Device Role : spare
    Array State : A.AA.A...A ('A' == active, '.' == missing)

Re: (help!) MD RAID6 won't --re-add devices?

[Bart Kus]

Things seem to have gone from bad to worse.  I upgraded to the latest 
mdadm, and it actually let me do an --add operation, but --re-add was 
still failing.  It added all the devices as spares though.  I stopped 
the array and tried to re-assemble it, but it's not starting.

jo ~ # mdadm -A /dev/md4 -f -u da14eb85:00658f24:80f7a070:b9026515
mdadm: /dev/md4 assembled from 5 drives and 5 spares - not enough to 
start the array.

How do I promote these "spares" to being the active decides they once 
were?  Yes, they're behind a few events, so there will be some data loss.

--Bart

On 1/13/2011 5:03 AM, Bart Kus wrote:
> Hello,
>
> I had a Port Multiplier failure overnight.  This put 5 out of 10 
> drives offline, degrading my RAID6 array.  The file system is still 
> mounted (and failing to write):
>
> Buffer I/O error on device md4, logical block 3907023608
> Filesystem "md4": xfs_log_force: error 5 returned.
> etc...
>
> The array is in the following state:
>
> /dev/md4:
>         Version : 1.02
>   Creation Time : Sun Aug 10 23:41:49 2008
>      Raid Level : raid6
>      Array Size : 15628094464 (14904.11 GiB 16003.17 GB)
>   Used Dev Size : 1953511808 (1863.01 GiB 2000.40 GB)
>    Raid Devices : 10
>   Total Devices : 11
>     Persistence : Superblock is persistent
>
>     Update Time : Wed Jan 12 05:32:14 2011
>           State : clean, degraded
>  Active Devices : 5
> Working Devices : 5
>  Failed Devices : 6
>   Spare Devices : 0
>
>      Chunk Size : 64K
>
>            Name : 4
>            UUID : da14eb85:00658f24:80f7a070:b9026515
>          Events : 4300692
>
>     Number   Major   Minor   RaidDevice State
>       15       8        1        0      active sync   /dev/sda1
>        1       0        0        1      removed
>       12       8       33        2      active sync   /dev/sdc1
>       16       8       49        3      active sync   /dev/sdd1
>        4       0        0        4      removed
>       20       8      193        5      active sync   /dev/sdm1
>        6       0        0        6      removed
>        7       0        0        7      removed
>        8       0        0        8      removed
>       13       8       17        9      active sync   /dev/sdb1
>
>       10       8       97        -      faulty spare
>       11       8      129        -      faulty spare
>       14       8      113        -      faulty spare
>       17       8       81        -      faulty spare
>       18       8       65        -      faulty spare
>       19       8      145        -      faulty spare
>
> I have replaced the faulty PM and the drives have registered back with 
> the system, under new names:
>
> sd 3:0:0:0: [sdn] Attached SCSI disk
> sd 3:1:0:0: [sdo] Attached SCSI disk
> sd 3:2:0:0: [sdp] Attached SCSI disk
> sd 3:4:0:0: [sdr] Attached SCSI disk
> sd 3:3:0:0: [sdq] Attached SCSI disk
>
> But I can't seem to --re-add them into the array now!
>
> # mdadm /dev/md4 --re-add /dev/sdn1 --re-add /dev/sdo1 --re-add 
> /dev/sdp1 --re-add /dev/sdr1 --re-add /dev/sdq1
> mdadm: add new device failed for /dev/sdn1 as 21: Device or resource busy
>
> I haven't unmounted the file system and/or stopped the /dev/md4 
> device, since I think that would drop any buffers either layer might 
> be holding.  I'd of course prefer to lose as little data as possible.  
> How can I get this array going again?
>
> PS: I think the reason "Failed Devices" shows 6 and not 5 is because I 
> had a single HD failure a couple weeks back.  I replaced the drive and 
> the array re-built A-OK.  I guess it still counted the failure since 
> the array wasn't stopped during the repair.
>
> Thanks for any guidance,
>
> --Bart
>
> PPS: mdadm - v3.0 - 2nd June 2009
> PPS: Linux jo.bartk.us 2.6.35-gentoo-r9 #1 SMP Sat Oct 2 21:22:14 PDT 
> 2010 x86_64 Intel(R) Core(TM)2 Quad CPU @ 2.40GHz GenuineIntel GNU/Linux
> PPS:  # mdadm --examine /dev/sdn1
> /dev/sdn1:
>           Magic : a92b4efc
>         Version : 1.2
>     Feature Map : 0x0
>      Array UUID : da14eb85:00658f24:80f7a070:b9026515
>            Name : 4
>   Creation Time : Sun Aug 10 23:41:49 2008
>      Raid Level : raid6
>    Raid Devices : 10
>
>  Avail Dev Size : 3907023730 (1863.01 GiB 2000.40 GB)
>      Array Size : 31256188928 (14904.11 GiB 16003.17 GB)
>   Used Dev Size : 3907023616 (1863.01 GiB 2000.40 GB)
>     Data Offset : 272 sectors
>    Super Offset : 8 sectors
>           State : clean
>     Device UUID : c0cf419f:4c33dc64:84bc1c1a:7e9778ba
>
>     Update Time : Wed Jan 12 05:39:55 2011
>        Checksum : bdb14e66 - correct
>          Events : 4300672
>
>      Chunk Size : 64K
>
>    Device Role : spare
>    Array State : A.AA.A...A ('A' == active, '.' == missing)
>
> -- 
> To unsubscribe from this list: send the line "unsubscribe linux-raid" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html

Re: (help!) MD RAID6 won't --re-add devices?

[Bart Kus]

Some research has revealed a frightening solution:

http://forums.gentoo.org/viewtopic-t-716757-start-0.html

That thread calls upon mdadm --create with the --assume-clean flag.  It 
also seems to re-enforce my suspicions that MD has lost my device order 
numbers when it marked the drives as spare (thanks, MD!  Remind me to 
get you a nice christmas present next year.).  I know the order of 5 out 
of 10 devices, so that leaves 120 permutations to try.  I've whipped up 
some software to generate all the permuted mdadm --create commands.

The question now: how do I test if I've got the right combination?  Can 
I dd a meg off the assembled array and check for errors somewhere?

The other question: Is testing incorrect combinations destructive to any 
data on the drives?  Like, would RAID6 kick in and start "fixing" parity 
errors, even if I'm just reading?

--Bart

On 1/15/2011 9:48 AM, Bart Kus wrote:
> Things seem to have gone from bad to worse.  I upgraded to the latest 
> mdadm, and it actually let me do an --add operation, but --re-add was 
> still failing.  It added all the devices as spares though.  I stopped 
> the array and tried to re-assemble it, but it's not starting.
>
> jo ~ # mdadm -A /dev/md4 -f -u da14eb85:00658f24:80f7a070:b9026515
> mdadm: /dev/md4 assembled from 5 drives and 5 spares - not enough to 
> start the array.
>
> How do I promote these "spares" to being the active decides they once 
> were?  Yes, they're behind a few events, so there will be some data loss.
>
> --Bart
>
> On 1/13/2011 5:03 AM, Bart Kus wrote:
>> Hello,
>>
>> I had a Port Multiplier failure overnight.  This put 5 out of 10 
>> drives offline, degrading my RAID6 array.  The file system is still 
>> mounted (and failing to write):
>>
>> Buffer I/O error on device md4, logical block 3907023608
>> Filesystem "md4": xfs_log_force: error 5 returned.
>> etc...
>>
>> The array is in the following state:
>>
>> /dev/md4:
>>         Version : 1.02
>>   Creation Time : Sun Aug 10 23:41:49 2008
>>      Raid Level : raid6
>>      Array Size : 15628094464 (14904.11 GiB 16003.17 GB)
>>   Used Dev Size : 1953511808 (1863.01 GiB 2000.40 GB)
>>    Raid Devices : 10
>>   Total Devices : 11
>>     Persistence : Superblock is persistent
>>
>>     Update Time : Wed Jan 12 05:32:14 2011
>>           State : clean, degraded
>>  Active Devices : 5
>> Working Devices : 5
>>  Failed Devices : 6
>>   Spare Devices : 0
>>
>>      Chunk Size : 64K
>>
>>            Name : 4
>>            UUID : da14eb85:00658f24:80f7a070:b9026515
>>          Events : 4300692
>>
>>     Number   Major   Minor   RaidDevice State
>>       15       8        1        0      active sync   /dev/sda1
>>        1       0        0        1      removed
>>       12       8       33        2      active sync   /dev/sdc1
>>       16       8       49        3      active sync   /dev/sdd1
>>        4       0        0        4      removed
>>       20       8      193        5      active sync   /dev/sdm1
>>        6       0        0        6      removed
>>        7       0        0        7      removed
>>        8       0        0        8      removed
>>       13       8       17        9      active sync   /dev/sdb1
>>
>>       10       8       97        -      faulty spare
>>       11       8      129        -      faulty spare
>>       14       8      113        -      faulty spare
>>       17       8       81        -      faulty spare
>>       18       8       65        -      faulty spare
>>       19       8      145        -      faulty spare
>>
>> I have replaced the faulty PM and the drives have registered back 
>> with the system, under new names:
>>
>> sd 3:0:0:0: [sdn] Attached SCSI disk
>> sd 3:1:0:0: [sdo] Attached SCSI disk
>> sd 3:2:0:0: [sdp] Attached SCSI disk
>> sd 3:4:0:0: [sdr] Attached SCSI disk
>> sd 3:3:0:0: [sdq] Attached SCSI disk
>>
>> But I can't seem to --re-add them into the array now!
>>
>> # mdadm /dev/md4 --re-add /dev/sdn1 --re-add /dev/sdo1 --re-add 
>> /dev/sdp1 --re-add /dev/sdr1 --re-add /dev/sdq1
>> mdadm: add new device failed for /dev/sdn1 as 21: Device or resource 
>> busy
>>
>> I haven't unmounted the file system and/or stopped the /dev/md4 
>> device, since I think that would drop any buffers either layer might 
>> be holding.  I'd of course prefer to lose as little data as 
>> possible.  How can I get this array going again?
>>
>> PS: I think the reason "Failed Devices" shows 6 and not 5 is because 
>> I had a single HD failure a couple weeks back.  I replaced the drive 
>> and the array re-built A-OK.  I guess it still counted the failure 
>> since the array wasn't stopped during the repair.
>>
>> Thanks for any guidance,
>>
>> --Bart
>>
>> PPS: mdadm - v3.0 - 2nd June 2009
>> PPS: Linux jo.bartk.us 2.6.35-gentoo-r9 #1 SMP Sat Oct 2 21:22:14 PDT 
>> 2010 x86_64 Intel(R) Core(TM)2 Quad CPU @ 2.40GHz GenuineIntel GNU/Linux
>> PPS:  # mdadm --examine /dev/sdn1
>> /dev/sdn1:
>>           Magic : a92b4efc
>>         Version : 1.2
>>     Feature Map : 0x0
>>      Array UUID : da14eb85:00658f24:80f7a070:b9026515
>>            Name : 4
>>   Creation Time : Sun Aug 10 23:41:49 2008
>>      Raid Level : raid6
>>    Raid Devices : 10
>>
>>  Avail Dev Size : 3907023730 (1863.01 GiB 2000.40 GB)
>>      Array Size : 31256188928 (14904.11 GiB 16003.17 GB)
>>   Used Dev Size : 3907023616 (1863.01 GiB 2000.40 GB)
>>     Data Offset : 272 sectors
>>    Super Offset : 8 sectors
>>           State : clean
>>     Device UUID : c0cf419f:4c33dc64:84bc1c1a:7e9778ba
>>
>>     Update Time : Wed Jan 12 05:39:55 2011
>>        Checksum : bdb14e66 - correct
>>          Events : 4300672
>>
>>      Chunk Size : 64K
>>
>>    Device Role : spare
>>    Array State : A.AA.A...A ('A' == active, '.' == missing)
>>
>> -- 
>> To unsubscribe from this list: send the line "unsubscribe linux-raid" in
>> the body of a message to majordomo@vger.kernel.org
>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>
> -- 
> To unsubscribe from this list: send the line "unsubscribe linux-raid" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html

Re: (help!) MD RAID6 won't --re-add devices?

[Jérôme Poulin]

On Sat, Jan 15, 2011 at 2:50 PM, Bart Kus <me@bartk.us> wrote:
> Some research has revealed a frightening solution:
>
> http://forums.gentoo.org/viewtopic-t-716757-start-0.html
>
> That thread calls upon mdadm --create with the --assume-clean flag.  It also
> seems to re-enforce my suspicions that MD has lost my device order numbers
> when it marked the drives as spare (thanks, MD!  Remind me to get you a nice
> christmas present next year.).  I know the order of 5 out of 10 devices, so
> that leaves 120 permutations to try.  I've whipped up some software to
> generate all the permuted mdadm --create commands.
>
> The question now: how do I test if I've got the right combination?  Can I dd
> a meg off the assembled array and check for errors somewhere?

I guess running a read-only fsck is the best way to proove it working.

>
> The other question: Is testing incorrect combinations destructive to any
> data on the drives?  Like, would RAID6 kick in and start "fixing" parity
> errors, even if I'm just reading?
>

If you don't want to risk your data, you could create a cowloop of
each device before writing to it, or dm snapshot using dmsetup.

I made a script for dmsetup snapshot on the side when I really needed
it because cowloop wouldn't compile. Here it is, it should help you
understand how it works!


RODATA=$1
shift
COWFILE=$1
shift
FSIZE=$1
shift
PREFIX=$1
shift

if [ -z $RODATA ] || [ -z $COWFILE ] || [ -z $FSIZE ] || [ ! -z $5 ]
then
	echo "Usage: $0 [read only device] [loop file] [size of loop in MB] {prefix}"
	echo "Read only device won't ever get a write."
	echo "Loop file can be a file or device where writes will be directed too."
	echo "Size is specified in MB, you will be able to write that much
change to the device created."
	echo "Prefix will get prepended to all devices created by this script
in /dev/mapper"
	exit -1
fi

MRODATA=$PREFIX${RODATA#/dev/}data
COWFILELOOP=$(losetup -f)
MCOWFILE=$PREFIX${RODATA#/dev/}cow
MSNAPSHOT=$PREFIX${RODATA#/dev/}snap


dd if=/dev/zero of=$COWFILE bs=1M seek=$FSIZE count=1
losetup $COWFILELOOP $COWFILE
echo "0 $(blockdev --getsz $RODATA) linear $RODATA 0" | dmsetup create $MRODATA
echo "0 $(blockdev --getsz $COWFILELOOP) linear $COWFILELOOP 0" |
dmsetup create $MCOWFILE
echo "0 $(blockdev --getsz /dev/mapper/$MRODATA) snapshot
/dev/mapper/$MRODATA /dev/mapper/$MCOWFILE p 64" | dmsetup create
$MSNAPSHOT

echo "You can now use $MSNAPSHOT for your tests, up to ${FSIZE}MB."
exit 0


> --Bart
>
--
To unsubscribe from this list: send the line "unsubscribe linux-raid" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html

Re: (help!) MD RAID6 won't --re-add devices? [SOLVED!]

[Bart Kus]

Thanks for the COW idea, had not thought of that.  Luckily, I had 10 
spare 2TB drives racked and powered, so I just backed up all the drives 
using dd.

Turns out a good way to test if you've got the right combination of 
drives is to do echo check > sync_action, wait 5 seconds, and then check 
mismatch_cnt.  If you've found the right combination, the count will be 
low or zero.

Another important thing to note is that "Version" reported by mdadm 
--detail /dev/mdX is NOT always the same as version reported by mdadm 
--examine /dev/sdX.  I guess array header and drive header track 
different version numbers.  My array header was reporting 1.02 while all 
the drives were showing 1.2.

And a key thing to know is that the default Data Offset has CHANGED over 
the years.  My original drives reported an offset of 272 sectors, and I 
believe the array was made with mdadm-2.6.6.  Using mdadm-3.1.4 to 
create a new array put the offset at 2048 sectors, a huge change!  Also, 
it seems when mdadm-3.1.4 added the old drives (272 offset at the time) 
into the array that was missing 5/10 drives and marked them as spares, 
the spare-marking process changed the offset to 384 sectors.  The array 
when created with mdadm-3.1.4 had actually reduced the Used Dev Size a 
bit from what the original array had, so none of the permutations worked 
since everything was misaligned.  I had to downgrade to mdadm-3.0 which 
created the array with the proper Dev Size and the proper Data Offset of 
272 sectors for the RAID6 blocks to line up.

Is there documentation somewhere about all these default changes?  I saw 
no options to specify the data offset either.  That would be a good 
option to add.

But best to add would be functional --re-add capability!  Reporting the 
array is "busy" when I'm trying to return its 5 missing drives isn't 
useful.  It should re-add its old drives as expected and flush any 
pending buffers.

Below is the (very hacky) code I used to test all the permutations of 
the 5 drives whose sequence was lost by being marked as spares.  
Hopefully it doesn't have to help anyone in the future.

#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/wait.h>

char *permutation[] = { "nopqr", "noprq", "noqpr", "noqrp", "norpq", 
"norqp", "npoqr", "nporq", "npqor", "npqro", "nproq", "nprqo", "nqopr", 
"nqorp", "nqpor", "nqpro", "nqrop", "nqrpo", "nropq", "nroqp", "nrpoq", 
"nrpqo", "nrqop", "nrqpo", "onpqr", "onprq", "onqpr", "onqrp", "onrpq", 
"onrqp", "opnqr", "opnrq", "opqnr", "opqrn", "oprnq", "oprqn", "oqnpr", 
"oqnrp", "oqpnr", "oqprn", "oqrnp", "oqrpn", "ornpq", "ornqp", "orpnq", 
"orpqn", "orqnp", "orqpn", "pnoqr", "pnorq", "pnqor", "pnqro", "pnroq", 
"pnrqo", "ponqr", "ponrq", "poqnr", "poqrn", "pornq", "porqn", "pqnor", 
"pqnro", "pqonr", "pqorn", "pqrno", "pqron", "prnoq", "prnqo", "pronq", 
"proqn", "prqno", "prqon", "qnopr", "qnorp", "qnpor", "qnpro", "qnrop", 
"qnrpo", "qonpr", "qonrp", "qopnr", "qoprn", "qornp", "qorpn", "qpnor", 
"qpnro", "qponr", "qporn", "qprno", "qpron", "qrnop", "qrnpo", "qronp", 
"qropn", "qrpno", "qrpon", "rnopq", "rnoqp", "rnpoq", "rnpqo", "rnqop", 
"rnqpo", "ronpq", "ronqp", "ropnq", "ropqn", "roqnp", "roqpn", "rpnoq", 
"rpnqo", "rponq", "rpoqn", "rpqno", "rpqon", "rqnop", "rqnpo", "rqonp", 
"rqopn", "rqpno", "rqpon" };

int main()
{
         int i, mismatches, status;
         FILE *handle;
         char command[1024];

         for (i = 0; i < sizeof permutation / sizeof (char *); i++) {
                 mismatches = -1; // Safety
                 sprintf(command, "/sbin/mdadm --create /dev/md4 
--assume-clean -R -e 1.2 -l 6 -n 10 -c 64 /dev/sda1 /dev/sd%c1 /dev/sdc1 
/dev/sdd1 /dev/sd%c1 /dev/sdm1 /dev/sd%c1 /dev/sd%c1 /dev/sd%c1 /dev/sdb1",
                         permutation[i][0], permutation[i][1], 
permutation[i][2], permutation[i][3], permutation[i][4]);
                 printf("Running: %s\n", command);
                 status = system(command);
                 if (WEXITSTATUS(status) != 0) {
                         printf("Command error\n");
                         return;
                 }
                 sleep(1);
                 handle = fopen("/sys/block/md4/md/sync_action", "w");
                 fprintf(handle, "check\n");
                 fclose(handle);
                 sleep(5);
                 handle = fopen("/sys/block/md4/md/mismatch_cnt", "r");
                 fscanf(handle, "%d", &mismatches);
                 fclose(handle);
                 printf("Permutation %s = %d mismatches\n", 
permutation[i], mismatches);
                 fflush(stdout);
                 sprintf(command, "/sbin/mdadm --stop /dev/md4");
                 printf("Running: %s\n", command);
                 status = system(command);
                 if (WEXITSTATUS(status) != 0) {
                         printf("Command error\n");
                         return;
                 }
                 sleep(1);

         }
}

The permutations I got from an online permutation generator:

http://users.telenet.be/vdmoortel/dirk/Maths/permutations.html

Didn't feel like writing that part of the algorithm.

--Bart


On 1/15/2011 4:05 PM, Jérôme Poulin wrote:
> On Sat, Jan 15, 2011 at 2:50 PM, Bart Kus<me@bartk.us>  wrote:
>> Some research has revealed a frightening solution:
>>
>> http://forums.gentoo.org/viewtopic-t-716757-start-0.html
>>
>> That thread calls upon mdadm --create with the --assume-clean flag.  It also
>> seems to re-enforce my suspicions that MD has lost my device order numbers
>> when it marked the drives as spare (thanks, MD!  Remind me to get you a nice
>> christmas present next year.).  I know the order of 5 out of 10 devices, so
>> that leaves 120 permutations to try.  I've whipped up some software to
>> generate all the permuted mdadm --create commands.
>>
>> The question now: how do I test if I've got the right combination?  Can I dd
>> a meg off the assembled array and check for errors somewhere?
> I guess running a read-only fsck is the best way to proove it working.
>
>> The other question: Is testing incorrect combinations destructive to any
>> data on the drives?  Like, would RAID6 kick in and start "fixing" parity
>> errors, even if I'm just reading?
>>
> If you don't want to risk your data, you could create a cowloop of
> each device before writing to it, or dm snapshot using dmsetup.
>
> I made a script for dmsetup snapshot on the side when I really needed
> it because cowloop wouldn't compile. Here it is, it should help you
> understand how it works!
>
>
> RODATA=$1
> shift
> COWFILE=$1
> shift
> FSIZE=$1
> shift
> PREFIX=$1
> shift
>
> if [ -z $RODATA ] || [ -z $COWFILE ] || [ -z $FSIZE ] || [ ! -z $5 ]
> then
> 	echo "Usage: $0 [read only device] [loop file] [size of loop in MB] {prefix}"
> 	echo "Read only device won't ever get a write."
> 	echo "Loop file can be a file or device where writes will be directed too."
> 	echo "Size is specified in MB, you will be able to write that much
> change to the device created."
> 	echo "Prefix will get prepended to all devices created by this script
> in /dev/mapper"
> 	exit -1
> fi
>
> MRODATA=$PREFIX${RODATA#/dev/}data
> COWFILELOOP=$(losetup -f)
> MCOWFILE=$PREFIX${RODATA#/dev/}cow
> MSNAPSHOT=$PREFIX${RODATA#/dev/}snap
>
>
> dd if=/dev/zero of=$COWFILE bs=1M seek=$FSIZE count=1
> losetup $COWFILELOOP $COWFILE
> echo "0 $(blockdev --getsz $RODATA) linear $RODATA 0" | dmsetup create $MRODATA
> echo "0 $(blockdev --getsz $COWFILELOOP) linear $COWFILELOOP 0" |
> dmsetup create $MCOWFILE
> echo "0 $(blockdev --getsz /dev/mapper/$MRODATA) snapshot
> /dev/mapper/$MRODATA /dev/mapper/$MCOWFILE p 64" | dmsetup create
> $MSNAPSHOT
>
> echo "You can now use $MSNAPSHOT for your tests, up to ${FSIZE}MB."
> exit 0
>
>
>> --Bart
>>
> --
> To unsubscribe from this list: send the line "unsubscribe linux-raid" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html

--
To unsubscribe from this list: send the line "unsubscribe linux-raid" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html

(help!) MD RAID6 won't --re-add devices?

[Bart Kus]

Hello,

I had a Port Multiplier failure overnight.  This put 5 out of 10 drives 
offline, degrading my RAID6 array.  The file system is still mounted 
(and failing to write):

Buffer I/O error on device md4, logical block 3907023608
Filesystem "md4": xfs_log_force: error 5 returned.
etc...

The array is in the following state:

/dev/md4:
         Version : 1.02
   Creation Time : Sun Aug 10 23:41:49 2008
      Raid Level : raid6
      Array Size : 15628094464 (14904.11 GiB 16003.17 GB)
   Used Dev Size : 1953511808 (1863.01 GiB 2000.40 GB)
    Raid Devices : 10
   Total Devices : 11
     Persistence : Superblock is persistent

     Update Time : Wed Jan 12 05:32:14 2011
           State : clean, degraded
  Active Devices : 5
Working Devices : 5
  Failed Devices : 6
   Spare Devices : 0

      Chunk Size : 64K

            Name : 4
            UUID : da14eb85:00658f24:80f7a070:b9026515
          Events : 4300692

     Number   Major   Minor   RaidDevice State
       15       8        1        0      active sync   /dev/sda1
        1       0        0        1      removed
       12       8       33        2      active sync   /dev/sdc1
       16       8       49        3      active sync   /dev/sdd1
        4       0        0        4      removed
       20       8      193        5      active sync   /dev/sdm1
        6       0        0        6      removed
        7       0        0        7      removed
        8       0        0        8      removed
       13       8       17        9      active sync   /dev/sdb1

       10       8       97        -      faulty spare
       11       8      129        -      faulty spare
       14       8      113        -      faulty spare
       17       8       81        -      faulty spare
       18       8       65        -      faulty spare
       19       8      145        -      faulty spare

I have replaced the faulty PM and the drives have registered back with 
the system, under new names:

sd 3:0:0:0: [sdn] Attached SCSI disk
sd 3:1:0:0: [sdo] Attached SCSI disk
sd 3:2:0:0: [sdp] Attached SCSI disk
sd 3:4:0:0: [sdr] Attached SCSI disk
sd 3:3:0:0: [sdq] Attached SCSI disk

But I can't seem to --re-add them into the array now!

# mdadm /dev/md4 --re-add /dev/sdn1 --re-add /dev/sdo1 --re-add 
/dev/sdp1 --re-add /dev/sdr1 --re-add /dev/sdq1
mdadm: add new device failed for /dev/sdn1 as 21: Device or resource busy

I haven't unmounted the file system and/or stopped the /dev/md4 device, 
since I think that would drop any buffers either layer might be 
holding.  I'd of course prefer to lose as little data as possible.  How 
can I get this array going again?

PS: I think the reason "Failed Devices" shows 6 and not 5 is because I 
had a single HD failure a couple weeks back.  I replaced the drive and 
the array re-built A-OK.  I guess it still counted the failure since the 
array wasn't stopped during the repair.

Thanks for any guidance,

--Bart

PPS: mdadm - v3.0 - 2nd June 2009
PPS: Linux jo.bartk.us 2.6.35-gentoo-r9 #1 SMP Sat Oct 2 21:22:14 PDT 
2010 x86_64 Intel(R) Core(TM)2 Quad CPU @ 2.40GHz GenuineIntel GNU/Linux
PPS:  # mdadm --examine /dev/sdn1
/dev/sdn1:
           Magic : a92b4efc
         Version : 1.2
     Feature Map : 0x0
      Array UUID : da14eb85:00658f24:80f7a070:b9026515
            Name : 4
   Creation Time : Sun Aug 10 23:41:49 2008
      Raid Level : raid6
    Raid Devices : 10

  Avail Dev Size : 3907023730 (1863.01 GiB 2000.40 GB)
      Array Size : 31256188928 (14904.11 GiB 16003.17 GB)
   Used Dev Size : 3907023616 (1863.01 GiB 2000.40 GB)
     Data Offset : 272 sectors
    Super Offset : 8 sectors
           State : clean
     Device UUID : c0cf419f:4c33dc64:84bc1c1a:7e9778ba

     Update Time : Wed Jan 12 05:39:55 2011
        Checksum : bdb14e66 - correct
          Events : 4300672

      Chunk Size : 64K

    Device Role : spare
    Array State : A.AA.A...A ('A' == active, '.' == missing)