[DRBD-user] Pool free report by drbdmanage can't be trust

Robert Altnoeder robert.altnoeder at linbit.com
Thu Feb 4 10:07:09 CET 2016

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

On 01/29/2016 11:08 AM, Julien Escario wrote:
> Le 25/01/2016 15:19, Julien Escario a écrit :
>> So I'm wondering how and when 'pool free' value is calculated. Is it
>> recalculated only when a new ressource is created ? deleted ?
It is normally recalculated whenever drbdmanage changes something that
modifies the amount of available space.

Another problem is that any backend that uses thin allocation
essentially returns data from fantasy land, so the pool free value in
drbdmanage will never be anything better than a rough estimate. Actually
allocating a volume of the reported free size might work or might not
work, depending on how much actual storage ends up being allocated upon
creating the resource on each node.
Right now, DRBD still full-syncs (which will also change in the future,
because obviously that does not make a lot of sense with thin
allocation), and drbdmanage does not yet have lots of logic for
estimating thin allocation, and for both reasons, all the values
returned by drbdmanage as it is now are usually very conservative and
fat-allocation-like regarding free space.
>> Is there a way to force it to rescan free space ? (with a dbus command perhaps ?)
>> That could perhaps be done by a cron job running at defined frequency ?
We have a prototype of a daemon that does something like that
(drbdmanage-poolmonitord). While update-pool always locks the control
volumes and updates pool data, the daemon uses a monitoring function
(the update_pool_check() D-Bus API) that first checks whether the amount
of space has changed, and only if it did, it triggers the update-pool
That will be released with some future release of drbdmanage, as it will
be especially useful if a storage pool is shared by drbdmanage and other

> Best regards,
> Julien Escario
Mit freundlichen Gruessen / Best regards,
: Robert Altnoeder
: Trainer / Developer
: LINBIT | Your Way to High Availability
: http://www.linbit.com

DRBD® and LINBIT® are registered trademarks of LINBIT. 

More information about the drbd-user mailing list