[Lustre-discuss] ldiskfs for MDT and zfs for OSTs?

Ned Bass bass6 at llnl.gov
Mon Oct 7 10:48:24 PDT 2013


On Mon, Oct 07, 2013 at 06:09:21AM -0400, Anjana Kar wrote:
> Is it possible to configure the MDT as ldiskfs and the OSTs with zfs
> in lustre 2.4? The server is running a lustre kernel on a Centos 6.4
> system, has both lustre-osd-ldiskfs and lustre-osd-zfs rpms installed.
> The MDT is up as ldiskfs, but get an error trying to configure the ost:
> 
> mkfs.lustre --fsname=lustrefs --reformat --ost --backfstype=zfs .....
> 
> mkfs.lustre FATAL: unable to prepare backend (22)
> mkfs.lustre: exiting with 22 (Invalid argument)

I suspect that the mkfs.lustre error is unrelated to the presence of an
ldiskfs MDT.  We need to see the complete command line parameters and
output to help you diagnose that problem.  It's often helpful to try
creating the pool and dataset "by hand" with zpool create and zfs
create, using the same names and devices.  It may reveal the problem
with an error message that is masked by mkfs.lustre.  Also check dmesg
to see if there was an error loading the ZFS module stack.

Having said all that, as Andreas said, you may run into other problems
running the ZFS and ldiskfs OSDs concurrently on the same node.  Using
separate MDS and OSS nodes is more likely to work, but this
configuration has not seen much testing.  So please report on your
experience if you go this route.

Thanks,
Ned



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