Lustre 1.6 Operations Manual

3. If you have a separate MGS (that you do not want to reformat), then add the
"writeconf" flag to mkfs.lustre on the MDT, run:
$ mkfs.lustre --reformat --writeconf –fsname spfs --mdt \
--mgs /dev/sda
Note – If you have a combined MGS/MDT, reformatting the MDT reformats the
MGS as well, causing all configuration information to be lost; you can start building
your new filesystem. Nothing needs to be done with old disks that will not be part
of the new filesystem, just do not mount them.
22.3.10 Reclaiming Reserved Disk Space
All current Lustre installations run the ext3 filesystem internally on service nodes.
By default, the ext3 reserves 5% of the disk space for the root user. In order to
reclaim this space, run the following command on your OSSs:
tune2fs [-m reserved_blocks_percent] [device]
You do not need to shut down Lustre before running this command or restart it
afterwards.
22.3.11 Considerations in Connecting a SAN with Lustre
Depending on your cluster size and workload, you may want to connect a SAN with
Lustre. Before making this connection, consider the following:
■ In many SAN filesystems without Lustre, clients allocate and lock blocks or
inodes individually as they are updated. The Lustre design avoids the high
contention that some of these blocks and inodes may have.
■
■
Lustre is highly scalable and can have a very large number of clients. SAN
switches do not scale to a large number of nodes, and the cost per port of a SAN
is generally higher than other networking.
Filesystems that allow direct-to-SAN access from the clients have a security risk
because clients can potentially read any data on the SAN disks, and misbehaving
clients can corrupt the filesystem for many reasons like improper filesystem,
network, or other kernel software, bad cabling, bad memory, and so on. The risk
increases with increase in the number of clients directly accessing the storage.
Chapter 22 Lustre Troubleshooting Tips 22-11