[DRBD-user] Migrating NFS to a DRBD block device

Jeff Buck jeffb at umci.com
Fri Oct 15 18:51:17 CEST 2004

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

OK, I know this would be a bit of a kludge, but wouldn't it work to put
LVM on top of the block device. Wouldn't the device number in that case
stay the same, even if you popped drbd in or out of the loop?

It would require a quick reconfigure of LVM every time, but you'd only
have to do some quick changes in the devices section.

The nice thing would be that you don't have to modify anything in the
kernel, or really modify any software at all. You could do it all
quickly and easily with a simple shell script.. Besides, LVM can be
handy later down the road as well.


On Fri, 2004-10-15 at 07:11, Bernd Schubert wrote:
> Hello,
> > NFS "handles" are in most implementations basically just
> >  <block device number>:<inode number>, which is supposed to be
> unique,
> > and  easily available.
> >
> > but this means that, if you change something on your nfs server,
> > and now the data is on some other block device (drbd), the block
> device
> > number changes, and thus all handles are invalid...
> >
> > if you change back, suddenly the handles are valid again.
> >
> > so there is no chance (without patching the nfs server to support a
> > configurable mapping of exported handle numbers to block dev
> numbers)
> > to migrate the data on the nfs server to some other block device
> without
> > rebooting / forcefully remounting the clients.
> I have currently not much time to give a detailed explanation how to
> solve 
> this, Omar, could you try to search via google for my name and 'fsid'?
> I have 
> answered this kind of question already at least two times in English. 
> If you shouldn't find it, I will try to answer more in detail in about
> 6-7 
> hours. 
> The basic idea is to fake the fsid via the fsid mount option. 
> You have to do this before you switch to drbd, so you set the fsid
> export 
> option, reexport, remount from your clients on the fly and finally can
> switch 
> the server to drbd.
> Cheers,
>  Bernd
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