On Wed, 2002-08-14 at 12:08, Greg Freemyer wrote:
> >> The normal way we setup something like this is to use a shared scsi
> >> or fiberchannel disk setup, that way you no longer have a singe
> >> point of failure. If you are putting the disks into one of the
> >> two computers then if that system goes down you are dead in the
> >> water. The other aspect of the above setup is using something
> >> like failsafe, the two nodes monitor each other, and can (if
> >> setup correctly) shoot the other node down and take over the
> >> filesystem if it detects problems. failsafe itself is opensource,
> >> not sure if the components of it which fail over the filesystem
> >> to the other node are. Of course all this assumes using the fs
> >> via NFS - the second node takes over the ip address of the failed
> >> node.
>
> >> A quick look at drbd on the net seems to show that it is designed
> >> for these sorts of setups, and it has links to all the high
> >> availability stuff for linux.
>
> >> That aside, there should be no problem doing this, provided you
> >> make sure the unmount from one system is complete before attempting
> >> to mount on the other system. Mounting a filesystem which is
> >> already mounted elsewhere is not a good thing, the second system
> >> will think the fs needs recovery running on it.
>
> >> Steve
>
> I don't think drbd is designed for use in a shared SCSI environment.
I did not intend to imply it was, just presenting a different way
to build a resilient configuration.
>
> It is more of a RAID 1 driver where the 2 halves of the mirror are on the 2
> different servers using internal disks.
>
> I believe it has support for ordered writes, but I for one would not simply
> assume XFS and drbd are compatible.
>
Ah, I should have read more.... if the fs is mirrored between the two
hosts then there is a chance it will work OK. However, the interesting
part of XFS is write ordering - there are certain writes which we need
to know have made it down to disk and will survive a crash. In this
sort of setup I really do not know where the data will be once drbd
says it is written. Probably still in cache on the remote box for a
start. There may well be circumstances where loss of both machines
will cause filesystem corruption.
you are right, testing such a setup before going live with it is
important, please do not take my comments as meaning it will definitely
work.
Steve
> Greg Freemyer
> Internet Engineer
> Deployment and Integration Specialist
> Compaq ASE - Tru64 v4, v5
> Compaq Master ASE - SAN Architect
> The Norcross Group
> www.NorcrossGroup.com
--
Steve Lord voice: +1-651-683-3511
Principal Engineer, Filesystem Software email: lord@xxxxxxx
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