[DRBD-user] External metadata size

Maros Timko timkom at gmail.com
Fri Mar 13 16:47:01 CET 2009


Thanks Lars,

please see comments below.
2009/3/13 Lars Ellenberg <lars.ellenberg at linbit.com>

> On Fri, Mar 13, 2009 at 11:01:05AM +0000, Maros Timko wrote:
> > Hi all,
> >
> > I wonder why user documentation states how to estimate required DRBD
> > metadata size for external metadata:
> >
> http://www.drbd.org/users-guide-emb/ch-internals.html#s-external-meta-data
> > when it is quite hardcoded value. At least example drbd.conf file still
> > includes this information (128MB for each DRBD resource).
>
> there is meta-disk, and there is flexible-meta-disk.
>
> man drbd.conf


Wow,
I thought flexible-meta-disk can be used for internal metadata only. I think
I saw it somewhere in my first contact with DRBD. Fine, now I checked man
drbd.conf and it in place since 8.2.6 so Mea Culpa. I should not simply lean
on template drbd.conf

>
> > So did ahything chance with DRBD 8.3.0 regarding external metadata size
> > requirements?
>
> with drbd 8.3, you can use up to 16 TiB storage (well, you should not
> have that exact amount, rather some sectors less).
>
> that would need 512 MiB worth of bitmap, plus the usual few KiB
> for "superblock" and activity log.
>

But then it is quite interesting. If I am using meta-disk I cannot attach
device that is larger then 4TB and if I want to, I simply have to use
flexible-meta-disk. I think I have a deja-vu from last December, there was a
messages exchange regarding mounting of 16TB devices.

What if I am using single LVM for multiple flexible-meta-disk devices
(flexible-meta-disk /dev/sda6[0...]) and later on I decide to resize/extend
the corresponding DRBD partitions - will this be handled by DRBD correctly
without any user intervention? Or -- from performance point of view -- would
it be prefarable to dump/import all the metadata blocks after such change?


>
> --
> : Lars Ellenberg
> : LINBIT | Your Way to High Availability
> : DRBD/HA support and consulting http://www.linbit.com
>
> DRBD® and LINBIT® are registered trademarks of LINBIT, Austria.
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