[DRBD-user] DRBD primary/primary vs. VMFS3 ?

pberton pascal.berton3 at free.fr
Mon Apr 4 18:33:32 CEST 2011

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

Hi folks!
I've read a few posts talking about DRBD vs. VMFS3, but none seem to answer
my question. May be someone can help. Here's the picture :
I'm thinking of a primary/primary config, with ESXs on both sides. If hosted
VMs do snapshots or make use of thin disks on both sides, corresponding
files will grow step by step or should I say, block by block, each new block
allocation being securized using SCSI reservations from the host running
that VM.
Now, guess 2 VMs on different sides of the replication chain make a new
block request at the same time. What would happen ? I suppose SCSI
reservations are not replicated by DRBD, therefore, each host will make its
own reservation and potentially allow the same block to both VMs leading to
corruption ?
Has anyone already played with this kind of architecture ? Is
primary/primary definitely a no-no for such architectures or is there some
magic feature that can help me out build something safe ?
Thanks by advance!
Best regards,
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