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Tue, 24 Jul 2007

Distributed storage competitors. DRBD.

I've just read a news on Kerneltrap about DRBD going upstream. DRBD is a Distributed Replicated Block Device, which allows to bind two remote storages to form a mirror. So far it only supports two nodes and has number of questionable own implementations of work queues, threads and locks. It is very big, I do not know why. It has 4gb limitation (u32 usage likely). There are problems with codying style.
That was problematic part, but drbd has a major advantage - it has a user base. I used drbd with heartbeat several years ago to create a high-availability cluster at one of the previous works. Although it was not very stable (sometimes it was not allowed to write to the system under resync, heartbeat did not detect fails and resync itself had problems), but it worked. So it is possible that it can be imported into the tree.
Unfortunately it was not posted neither to netdev@ nor to linux-fsdevel@, so I can not comment on that (although I'm not sure my comments would be understood correctly, but not as advertising of my work :).

So, right now I'm keeping silence about drbd and instead will think about how to better work with block requests, which cross the boundary between nodes, so that as much as possible allocations would be eliminated.
During that I found a perfect way to make a multi-node mirror, btw, but so far I will postpone its implementation.

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