[DRBD-user] dual primary mode with which FS

Christian Iversen chrivers at iversen-net.dk
Wed Mar 24 10:52:30 CET 2010

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

On 2010-03-24 10:42, Stefan Seifert wrote:
> On Wednesday 24 March 2010 09:50:44 Christian Iversen wrote:
>> Are you sure that LVM can create the snapshot without updating the
>> metadata on the device? Because that's not allowed.
> Actually it never occurred to me that LVM could change the volume. But I could
> not imagine any reason for it to do that. And indeed I'm using snapshots for
> backing up my DRBD volumes without any problem, so my guess should be correct.

Well not the volume as such, just the LVM metadata around the volume (I 
assume you mean the fs volume, on top of LVM, on top of DRBD).

I meant the question rhetorically. Snapshotting *definitely* causes 
writes to the LVM volumes. Now, these volumes are only updated when you 
do the LVM changes, not when you work on the volume, so you might be 
lucky that no 2 changes occur at the same time, but without some sort of 
lucking mechanism (think cLVM), you're really just playing on luck.

And again, if you use cLVM, that's a clustered file system (yes, LVM is 
a filesystem), and we're back to the beginning again.

In short: you cannot use normal filesystems on DRBD in primary-primary mode.

Med venlig hilsen
Christian Iversen

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