/dev/nerd

In my adventures with DRBD I recently ran across this error that took me a couple days to resolve:

d(data) 1: Failure: (114) Lower device is already claimed. This usually means it is mounted.

[data] cmd /sbin/drbdsetup 1 disk /dev/sdb /dev/sdb internal –set-defaults –create-device –on-io-error=detach –no-disk-barrier –no-disk-flushes  failed – continuing!

I was a bit confused since the filesystem wasn’t mounted anywhere (mount showed only the system volumes) and there weren’t any other programs using the raw disk.

Creating a filesystem also ran into a similar error:

/dev/sdb is apparently in use by the system; will not make a filesystem here

Obviously this is not just a problem with drbd.

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My application:

I’m in the process of playing with DRBD with a couple spare servers in my garage. The idea being that while my business is far too poor to afford a SAN, a DRBD cluster should be able to exceed my needs for semi-redundant storage.

Part of DRBD involves a link between the two servers for synchronization (basically copying over bits that change). This is preferably a private link so that your primary connection doesn’t see bandwidth contention during heavy writes, so for testing purposes I tossed a couple dual port Intel NICs I had laying around into the servers so that I could have a dedicated 2 gbit synchronization link.

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