Re: Understanding raid array status: Active vs Clean

[George Duffield <forumscollective@gmail.com>]

# cat /sys/block/md0/md/safe_mode_delay returns:

0.203

changing the value to 0.500:
# echo 0.503 > /sys/block/md0/md/safe_mode_delay

makes no difference to the array state.



On Wed, Jun 18, 2014 at 5:57 PM, George Duffield
<forumscollective@gmail.com> wrote:
> Thx Robin
>
> I've run:
> # mdadm --manage /dev/md0 --re-add /dev/sdb1
> mdadm: re-added /dev/sdb1
>
> # mdadm --detail /dev/md0 now returns:
>
> /dev/md0:
>         Version : 1.2
>   Creation Time : Thu Apr 17 01:13:52 2014
>      Raid Level : raid5
>      Array Size : 11720536064 (11177.57 GiB 12001.83 GB)
>   Used Dev Size : 2930134016 (2794.39 GiB 3000.46 GB)
>    Raid Devices : 5
>   Total Devices : 5
>     Persistence : Superblock is persistent
>
>   Intent Bitmap : Internal
>
>     Update Time : Wed Jun 18 19:46:38 2014
>           State : active
>  Active Devices : 5
> Working Devices : 5
>  Failed Devices : 0
>   Spare Devices : 0
>
>          Layout : left-symmetric
>      Chunk Size : 512K
>
>            Name : audioliboffsite:0  (local to host audioliboffsite)
>            UUID : aba348c6:8dc7b4a7:4e282ab5:40431aff
>          Events : 11319
>
>     Number   Major   Minor   RaidDevice State
>        0       8       17        0      active sync   /dev/sdb1
>        1       8       65        1      active sync   /dev/sde1
>        2       8       81        2      active sync   /dev/sdf1
>        3       8       33        3      active sync   /dev/sdc1
>        5       8       49        4      active sync   /dev/sdd1
>
>
> # watch cat /proc/mdstat returns:
>
> Personalities : [raid6] [raid5] [raid4]
> md0 : active raid5 sdb1[0] sdd1[5] sdc1[3] sde1[1] sdf1[2]
>       11720536064 blocks super 1.2 level 5, 512k chunk, algorithm 2
> [5/5] [UUUUU]
>       bitmap: 0/22 pages [0KB], 65536KB chunk
>
> unused devices: <none>
>
>
> # watch -d 'grep md0 /proc/diskstats' returns:
>    9       0 md0 348 0 2784 0 0 0 0 0 0 0 0
>
> and the output never changes.
>
> So, array seems OK, and I'm back to the question that started this
> thread - why would this array's state be Active rather than Clean?
>
>
>
>
> On Wed, Jun 18, 2014 at 5:03 PM, Robin Hill <robin@robinhill.me.uk> wrote:
>> On Wed Jun 18, 2014 at 03:25:27PM +0200, George Duffield wrote:
>>
>>> A little more information if it helps deciding on the best recovery
>>> strategy.  As can be seen all drives still in the array have event
>>> count:
>>> Events : 11314
>>>
>>> The drive that fell out of the array has an event count of:
>>> Events : 11306
>>>
>>> Unless mdadm writes to the drives when a machine is booted or the
>>> array partitioned I know for certain that the array has not been
>>> written to i.e. no files have been added or deleted.
>>>
>>> Per https://raid.wiki.kernel.org/index.php/RAID_Recovery it would seem
>>> to me the following guidance applies:
>>> If the event count closely matches but not exactly, use "mdadm
>>> --assemble --force /dev/mdX <list of devices>" to force mdadm to
>>> assemble the array anyway using the devices with the closest possible
>>> event count. If the event count of a drive is way off, this probably
>>> means that drive has been out of the array for a long time and
>>> shouldn't be included in the assembly. Re-add it after the assembly so
>>> it's sync:ed up using information from the drives with closest event
>>> counts.
>>>
>>> However, in my case the array has been auto assebled by mdadm at boot
>>> time.  How would I best go about adding /dev/sdb1 back into the array?
>>>
>> That doesn't matter here - a force assemble would have left out the
>> drive with the lower event count as well. As there's a bitmap on the
>> array then either a --re-add or a --add (these should be treated the
>> same for arrays with persistent superblocks) should just synch any
>> differences since the disk was failed.