Lustre 1.6 Operations Manual

4.1.1 MountConf
MountConf is shorthand for Mount Configuration. The Lustre cluster is configured
only by the mkfs.lustre and mount commands. The MountConf system is one of the
important features of Lustre 1.6.x.
MountConf involves userspace utilities (mkfs.lustre, tunefs.lustre, mount.lustre, lctl)
and two new OBD types, the MGC and MGS. The MGS is a configuration
management server, which compiles configuration information about all Lustre
filesystems running at a site. There should be one MGS per site, not one MGS per
filesystem. The MGS requires its own disk for storage. However, there is a provision
to allow the MGS to share a disk ("co-locate") with an MDT of one filesystem.
You must start the MGS first as it manages the configurations. Beyond this, there are
no ordering requirements to when a Target (MDT or OST) can be added to a
filesystem. (However, there should be no client I/O at addition time, also known as
"quiescent ost addition.")
For example, consider the following order of starting the servers.
1. Start the MGS (start mgs)
2. Mount OST 1 (mkfs, mount ost #1)
3. Mount the MDT (mkfs, mount mdt)
4. Mount OST 2 (mkfs, mount ost #2)
5. Mount the client (mount client)
6. Mount OST 3 (mkfs, mount ost #3)
The clients and the MDT are notified that there is a new OST on-line and they can
use it immediately.
Note – The MGS must be running before any new servers are added to the
filesystem. After the servers start the first time, they cache a local copy of their
startup logs so they can restart with or without the MGS.
Currently, there is nothing actually visible on a server mount point (but df will
show free space). Eventually, the mount point will probably look like a Lustre client.
Chapter 4 Lustre Installation 4-3