[DRBD-user] mke2fs issues an unused block warning when creating drbd0

Lars Ellenberg lars.ellenberg at linbit.com
Fri Dec 11 13:47:33 CET 2015

Note: "permalinks" may not be as permanent as we would like,
direct links of old sources may well be a few messages off.

On Wed, Dec 09, 2015 at 04:13:15PM +0000, Dischino, Chris wrote:
> On a VM,  when we go to create the drbd0 file system,  mke2fs writes
> out a warning,47 blocks unused.  Using tune2fs -l, both drbd0, and the
> physical device sda6,  have a block count of 14909440  and a block
> size of 4096.  From my calculations below,  it looks like  drbd meta
> data has included the 47 unused blocks and the file system has not.  I
> have never seen "warning: 47 blocks unused" message before.  Not sure
> if it is related to the VM, the size of the partition.  Does anyone
> know what this warning is trying to tell me ?  Any thought on why
> mke2fs would not use all the blocks ?  No bad blocks were detected.
> When I calculate the size of the meta data, it seem to include the
> unused blocks, do you know if this is correct ?  Do  I need to specify
> the number of blocks for this case, when creating the drbd device ?
> Any information would be greatly appreciated.
> /Chris
> Sonus Networks
> [root at SUZUKA05 sonus]# /sbin/mke2fs -j /dev/drbd0 | colcrt -  2> /tmp/cld.txt
> mke2fs 1.42.5 (29-Jul-2012)
> warning: 47 blocks unused.

Normal "rounding" behaviour of mke2fs.
It calculates block size, number of blocks per group,
and number of block groups, and some other stuff,
and may decide to not use a partial block group.

In your case, it decides to use 455 block groups, with 32768 blocks per group,
resulting in 455 * 32768 blocks of 4kB each, leaving 188kB or 47 blocks unused.

Try with a loop device of specific size,
or with some other partition of "odd" size,
and you'll get similar results.

Nothing to do with DRBD.

: Lars Ellenberg
: http://www.LINBIT.com | Your Way to High Availability
: DRBD, Linux-HA  and  Pacemaker support and consulting

DRBD® and LINBIT® are registered trademarks of LINBIT, Austria.
please don't Cc me, but send to list   --   I'm subscribed

More information about the drbd-user mailing list