Re: Unable to reduce raid size.

[NeilBrown <neilb@suse.de>]

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On Fri, 18 Jul 2014 10:50:54 +0200 Killian De Volder
<killian.de.volder@megasoft.be> wrote:

> Hello,
> 
> I have a strange issue, I cannot reduce the size of a degraded raid 5:
> 
> strace mdadm -vv --grow /dev/md125 --size=2778726400
> 
> Fails with:
> Stace:
>     open("/sys/block/md125/md/dev-sdb4/size", O_WRONLY) = 4
>     write(4, "2778726400", 10)              = -1 EBUSY (Device or resource busy)
>     close(4)

This condition isn't treated as an error by mdadm, so it isn't the cause.

Could you post the entire strace (really, bytes a cheap, alway provide more
detail than you think is needed.... though you did provide quite a bit)

Any kernel messages (dmesg output) ??

NeilBrown


> Stdout:
>     component size of /dev/md125 unchanged at 2858285568K
> Stderr:
>     <nothing>
> 
> 
> Any suggestions ?
> Note: I can work around this bug, by moving partitions around a bit, and not requiring the size reduction.
> However I suspect a bug/undocumented border case that should be resolved?
> 
> 
> Things I tried:
> ---------------
> - Disable bcache udev rules (as it was appearing in each attempt, maybe it got triggered during resize, seems not to be the case).
> - I have tried the same with loop files -> this works fine even with bcache (and the udev rules disabled)
> - Removed the internal write bitmap
> - Opend the file os.open("md125",os.O_EXCL,os.O_RDWR) in Python to test if it's in use somewhere (command worked fine)
> - Set array-size to the less then the desired new size (while still not destroying the FS below it).
> 
>  
> Information:
> ------------
> Kernel version: 3.15.5
> mdadm tools: 3.3-r2
> 
> mdadm --detail:
> /dev/md125:
>         Version : 1.2
>   Creation Time : Wed Apr 16 20:58:09 2014
>      Raid Level : raid5
>      Array Size : 8283750400 (7900.00 GiB 8482.56 GB)
>   Used Dev Size : 2858285568 (2725.87 GiB 2926.88 GB)
>    Raid Devices : 4
>   Total Devices : 3
>     Persistence : Superblock is persistent
> 
>     Update Time : Fri Jul 18 09:53:08 2014
>           State : clean, degraded
>  Active Devices : 3
> Working Devices : 3
>  Failed Devices : 0
>   Spare Devices : 0
> 
>          Layout : left-symmetric
>      Chunk Size : 512K
> 
>            UUID : 885c588b:c3503d9d:c67b86db:2887f8f7
>          Events : 6440
> 
>     Number   Major   Minor   RaidDevice State
>        0       8       36        0      active sync   /dev/sdc4
>        2       0        0        2      removed
>        2       8       20        2      active sync   /dev/sdb4
>        4       8       52        3      active sync   /dev/sdd4
> 


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