Re: MD RAID Bug 7/15/12

[NeilBrown <neilb@suse.de>]

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On Sat, 29 Sep 2012 17:12:40 -0700 Mark Munoz
<mark.munoz@rightthisminute.com> wrote:

> Hi I appear to have been affected by the bug you found on 7/15/12.  The data I have on this array is really important and I want to make sure I get this correct before I actually make changes.
> 
> Configuration:
> md0 is a RAID 6 volume with 24 devices and 1 spare.  It is working fine and was unaffected.
> md1 is a RAID 6 volume with 19 devices and 1 spare.  It was affected.  All the drives show as unknown raid level and 0 devices.  With the exception of device 5.  It has all the information.
> 
> Here is the output from that drive:
> 
> serveradmin@hulk:/etc/mdadm$ sudo mdadm --examine /dev/sdaf
> /dev/sdaf:
>           Magic : a92b4efc
>         Version : 1.2
>     Feature Map : 0x0
>      Array UUID : 6afb3306:144cec30:1b2d1a19:3a56f0d3
>            Name : hulk:1  (local to host hulk)
>   Creation Time : Wed Aug 15 16:25:30 2012
>      Raid Level : raid6
>    Raid Devices : 19
> 
>  Avail Dev Size : 5860531120 (2794.52 GiB 3000.59 GB)
>      Array Size : 99629024416 (47506.82 GiB 51010.06 GB)
>   Used Dev Size : 5860530848 (2794.52 GiB 3000.59 GB)
>     Data Offset : 2048 sectors
>    Super Offset : 8 sectors
>           State : clean
>     Device UUID : 205dfd9f:9be2b9ca:1f775974:fb1b742c
> 
>     Update Time : Sat Sep 29 12:22:51 2012
>        Checksum : 9f164d8e - correct
>          Events : 38
> 
>          Layout : left-symmetric
>      Chunk Size : 4K
> 
>    Device Role : Active device 5
>    Array State : AAAAAAAAAAAAAAAAAAA ('A' == active, '.' == missing)
> 
> Now I also have md2 which is a striped RAID of both md0 and md1.
> 
> When I type:
> 
> sudo mdadm --create --assume-clean /dev/md1 --level=6 --chunk=4 --metadata=1.2 --raid-devices=19 /dev/sdaa /dev/sdab /dev/sdac /dev/sdad /dev/sdae /dev/sdaf /dev/sdag /dev/sdah /dev/sdai /dev/sdaj /dev/sdak /dev/sdal /dev/sdam /dev/sdan /dev/sdao /dev/sdap /dev/sdaq /dev/sdar /dev/sdas
> 
> the following error for each device.
> 
> mdadm: /dev/sdaa appears to be part of a raid array:
>     level=-unknown- devices=0 ctime=Wed Aug 15 16:25:30 2012
> mdadm: partition table exists on /dev/sdaa but will be lost or
>        meaningless after creating array
> 
> I want to make sure by running this above command that I won't affect any of the data of md2 when I assemble that array after creating md1.  Any help on this issue would be greatly appreciated.  I would normally just DD copies but as you can see I would have to buy 19 more 3TB hard drives as well as the time to DD each drive.  It is a production server and that kind of down time would really rather be avoided.  

Running this command will only overwrite the 4K of metadata, 4K from the
start of the devices.  It will not write anything else to any device.

so yes, it is safe.

NeilBrown



> 
> Thank you so much for your time.
> 
> Mark Munoz
> 623.523.3201--
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