[DRBD-user] Question on ext3 and dual primaries mode

Florian Haas florian.haas at linbit.com
Mon Sep 14 10:23:09 CEST 2009

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

On 2009-09-14 10:20, Mark Watts wrote:
> Looking back on my notes, I'm totally wrong here. DRBD/Xen live
> migration does NOT involve ext3. I'm thinking about something entirely
> different.
> http://www.drbd.org/users-guide/ch-xen.html
> ext3 + allow-two-primaries will destroy data.
> /me goes for coffee.

Mark just beat me for the correction. :)

I'm 100% positive Mark is well aware of what follows, but just in case
some is pulling this thread from the list archives:

In the case Mark describes (which is documented in the User's Guide
chapter he mentioned in his follow up), you would not have ext3 directly
on top of your DRBD device. Instead, your DRBD resource would be
configured to act as a Virtual Block Device for Xen, that VBD would most
likely contain a partition table, and you'd have ext3 inside one of the
partitions. Which means that as long as you have Xen behaving correctly
you're fine. And which also means it's actually rather hard to mount the
ext3 filesystem from within your host, as it requires a kpartx detour
which makes it a little harder shooting yourself in the foot.

Having ext3 right inside dual-Primary DRBD, by contrast, makes it really
easy to shoot yourself in the foot, and royally mess up your data. Don't
do that.


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