[DRBD-user] increasing drbd device size

Lars Ellenberg lars.ellenberg at linbit.com
Thu Apr 26 11:26:26 CEST 2007

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

On Mon, Apr 23, 2007 at 06:53:47AM +0000, manjo wrote:
> After adding larger drives (750G) to my drbd setup and resyncing,
> the drbd device still shows old size of 500G. However the underlying 
> filesystem, reiserfs on linux raid1, shows the new size of 750G. What 
> should be my next step? Do I need to shrink the filesystem by 128 M?

> Thanks. Since I already have the underlying filesystem resized, I am 
> guessing I do not have to call resize_reiserfs command on the drives 
> *after* I call drbdadm resize. Or do I?

no offense.

but you got it all seriously backwards.

there is no "underlying file system".

there is the physical block device.
there may be some abstraction block device layers (evms, lvm etc).
then there is drbd.
still block device.
no file system yet.

then, on the drbd, there is your file system.

if you add more physical storage,
you propagate that change up the stack:
tell the abstraction layers, if any,
that there is more physical storage.

then tell drbd that the lower level devices are larger now.

on both nodes.

verify that it indeed now announces the expected size.

and only then,
and not one second before,
tell the file system about it.

(btw, if you want to reduce space, you do it from top to bottom,
 first reducing the file system size, if it supports that,
 then reduce drbd, then the abstraction layers if any, and then
 the physical drives.)

whatever you did to get your file system bigger than the drbd device:
you seriouly screwed up, bypassing drbd.
you need to make sure that you access the data you want to be mirrored
by drbd only through drbd, otherwise it cannot help you.

now, you definetly need a full sync to be sure both parts of the drbd
mirror are identical again.

: Lars Ellenberg                            Tel +43-1-8178292-0  :
: LINBIT Information Technologies GmbH      Fax +43-1-8178292-82 :
: Vivenotgasse 48, A-1120 Vienna/Europe    http://www.linbit.com :
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