[zfs-discuss] DRBD or AVS with ZFS

Alexander Schreiber als at thangorodrim.de
Tue Oct 4 03:15:19 EDT 2011


On Mon, Oct 03, 2011 at 06:31:06PM -0700, Mike Gracy wrote:
> You should never do a mkfs on any zfs volume. I never said that. I just
> wondering aloud if dbrd was completely fs agnostic.

Yes, it is. DRBD is just what it says on the tin: a Distributed Replicated
_Block_ Device. It doesn't care what you use it for.

> Reading docs over at dbrd make me think that this is intercepting the
> kernel's write to the disk and send a copy to a receiver on another machine
> with the same setup.

No intercepting involved. You use the /dev/drbdX device just like any other
block device (say, /dev/sdb2). You can put a filesystem on it, use it for
swap, ... whatever. I/O goes to the drbd device, which gets handled by the
drbd driver. Lets assume you've configured drbd for synchronous mode (which
is the only sane choice if you care for your data at all). For writes, they
go to the drbd device, the drbd driver sends one write to the local disk and
a copy of the same write to the remote disk over the network. When both write
calls (local & remote backing store) return, then the write to the drbd
device returns. Reads are usually (assuming no breakage) satisfied from
local disk or (in case of disk failure) from whatever backing store is still
available.

Kind regards,
            Alex.
-- 
"Opportunity is missed by most people because it is dressed in overalls and
 looks like work."                                      -- Thomas A. Edison



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