Re: Write intent bitmaps.

["NeilBrown" <neilb@suse.de>]

On Tue, August 25, 2009 12:39 am, Simon Jackson wrote:
>
>
> I am trying to use write intent bitmaps on some RAID 1 volumes to reduce
> the rebuild times in the event of hard resets that cause the md driver to
> kick members out of my arrays.
>
> I used the mdadm --grow /dev/md0 --bitmap=internal  and this appeared to
> succeed, but when I tried to examine the bitmap I get an error.
>
>
> :~$ sudo mdadm --grow /dev/md0 --bitmap=internal
> :~$ sudo mdadm -X /dev/md0
>         Filename : /dev/md0
>            Magic : 00000000
> mdadm: invalid bitmap magic 0x0, the bitmap file appears to be corrupted
>          Version : 0
> mdadm: unknown bitmap version 0, either the bitmap file is corrupted or
> you need to upgrade your tools

Quoting from the man page:

       -X, --examine-bitmap
              Report  information about a bitmap file.  The argument is
either
              an external bitmap file or an array  component  in  case  of
 an
              internal  bitmap.   Note  that  running  this on an array
device
              (e.g.  /dev/md0) does not report the bitmap for that array.


Particularly read the last sentence.
Then try
   mdadm -X /dev/sda5

NeilBrown


>
> cat /proc/mdstat
> Personalities : [raid1]
>
> md0 : active raid1 sda5[0] sdb5[1]
>       7823552 blocks [2/2] [UU]
>       bitmap: 29/239 pages [116KB], 16KB chunk
>
> unused devices: <none>
> sjackson@mercuryst5:~$ sudo mdadm -X /dev/md0
>         Filename : /dev/md0
>            Magic : 00000000
> mdadm: invalid bitmap magic 0x0, the bitmap file appears to be corrupted
>          Version : 0
> mdadm: unknown bitmap version 0, either the bitmap file is corrupted or
> you need to upgrade your tools
>
> Do I really have a usable bitmap on the device in this case?
>
> Thanks for any input.
>
>
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