HP ProLiant DL380G5-WSS 3.7.0 HP StorageWorks HP Scalable NAS File Serving Sof - Page 123
Filesystem synchronization and device locking, Recover from a server shutdown, Filesystem quotas
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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) daemon 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. Recover from a server shutdown When a server using a PSFS filesystem either shuts down unexpectedly or stops communicating with the cluster, another server in the cluster will replay the filesystem journal to complete any transactions that were in progress at the time of the shutdown. Users on the remaining servers will notice a slight delay while the journal is replayed. Typically the recovery procedure takes only a few seconds. The recovery process restores only the structural metadata information. Any regular file data in the blocks that were in use when the shutdown occurred may be corrupted or lost. The server that crashed or lost communication with the cluster will not be able to access the filesystem until it is rebooted. Filesystem quotas The PSFS filesystem supports hard and soft quotas for users and groups. A hard quota specifies the maximum amount of disk space in a particular filesystem that can be used by files owned by the user or group. A soft limit is typically set below the hard limit and triggers a warning when it is reached. HP Scalable NAS File Serving Software administration guide 123