Lustre 1.6 Operations Manual

How can I check if a filesystem is active (the MGS, MDT and OSTs are
all online)?
You can look at /proc/fs/lustre/lov/*/target_obds for "ACTIVE" vs "INACTIVE"
on MDS/clients.
How to reclaim the 5 percent of disk space reserved for root?
If your filesystem normally looks like this:
$ df -h /mnt/lustre
Filesystem Size Used Avail Use% Mounted on
databarn 100G 81G 14G 81% /mnt/lustre
You might be wondering: where did the other 5 percent go? This space is reserved
for the root user.
Currently, all Lustre installations run the ext3 filesystem internally on service nodes.
By default, ext3 reserves 5 percent of the disk for the root user.
To reclaim this space for use by all users, run this command on your OSSs:
tune2fs [-m reserved_blocks_percent] [device]
This command takes effect immediately. You do not need to shut down Lustre
beforehand or restart Lustre afterwards.
Why are applications hanging?
The most common cause of hung applications is a timeout. For a timeout involving
an MDS or failover OST, applications attempting to access the disconnected resource
wait until the connection is re-established.
In most cases, applications can be interrupted after a timeout with the KILL, INT,
TERM, QUIT, or ALRM signals. In some cases, for a command which communicates
with multiple services in a single system call, you may have to wait for multiple
timeouts.
Appendix D Lustre Knowledge Base D-3