Re: Write intent bitmaps.

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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