4.1.0 HP PolyServe Matrix Server administration guide (T5392-96073, October 2010)

• Coordinates filesystem mounts, unmounts, and crash recovery operations.
• Checks for cluster partitioning, which can occur when cluster network communic-
ations are lost but the affected servers can still access the SAN. If this situation
occurs, Matrix Server determines which servers should continue to have SAN
access and excludes the other servers from the SAN. This step prevents data
corruption from occurring.
• Communicates filesystem status to the PolyServe Management Console. It reports
both the global status of a filesystem (for example, whether it is up or going
through a recovery operation) and the status of the filesystem on each server (for
example, whether the filesystem is mounted or unmounted).
Filesystem synchronization and device locking
The Distributed Lock Manager (DLM) process coordinates access to shared resources
in the cluster. To do this, it provides the locking mechanisms used to implement the
necessary synchronization for various filesystem operations. (Filesystem operations
include, but are not limited to, filesystem mounts, reads and writes of files, and the
initial creation of a filesystem.)
The operating system kernel uses the DLM to obtain the appropriate lock(s) for all
access and modification of files within a PSFS filesystem, ensuring that all PSFS
filesystem data are coherent across the cluster. Similarly, the PSFS operations to
create, mount, or fsck a filesystem are mutually exclusive, and also use the DLM
locking mechanisms.
The DLM provides the fundamental locking mechanisms to prevent mutually exclusive
operations from occurring at the same time within the cluster, while allowing
operations that can be performed concurrently to proceed in parallel.
Disk quotas
Disk quotas are enabled or disabled at the filesystem level. When quotas are enabled,
the filesystem performs quota accounting to track the disk use of each user having
an assigned disk quota.
When you create a filesystem and enable quotas, you can also set options including
the default hard and soft limits for users on the filesystem. A hard limit specifies the
maximum amount of disk space in the filesystem that can be used by files owned by
the user. A soft limit is typically set below the hard limit and triggers a warning when
it is reached.
If you choose to enforce hard limits, when a file owner reaches the hard limit, the
filesystem will not allow the owner to create files or increase the size of an existing
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