VERITAS File SystemÖ 3.5 (HP OnlineJFS/JFS3.5) AdministratorÆs Guide (December 2002)

147
Glossary
access control list (ACL) The information that identifies specific users or groups and their access
privileges for a particular file or directory.
agent A process that manages predefined VERITAS Cluster Server (VCS) resource types. Agents bring
resources online, take resources offline, and monitor resources to report any state changes to VCS. When an
agent is started, it obtains configuration information from VCS and periodically monitors the resources and
updates VCS with the resource status.
allocation unit A group of consecutive blocks on a file system that contain resource summaries, free
resource maps, and data blocks. Allocation units also contain copies of the super-block.
asynchronous writes A delayed write in which the data is written to a page in the system’s page cache, but
is not written to disk before the write returns to the caller. This improves performance, but carries the risk of
data loss if the system crashes before the data is flushed to disk.
atomic operation An operation that either succeeds completely or fails and leaves everything as it was
before the operation was started. If the operation succeeds, all aspects of the operation take effect at once and
the intermediate states of change are invisible. If any aspect of the operation fails, then the operation aborts
without leaving partial changes.
Block-Level Incremental Backup (BLI Backup) A VERITAS backup capability that does not store and
retrieve entire files. Instead, only the data blocks that have changed since the previous backup are backed up.
buffered I/O During a read or write operation, data usually goes through an intermediate kernel buffer
before being copied between the user buffer and disk. If the same data is repeatedly read or written, this
kernel buffer acts as a cache, which can improve performance. See unbuffered I/O and direct I/O.
CFS VERITAS Cluster File System.
cluster mounted file system A shared file system that enables multiple hosts to mount and perform file
operations on the same file. A cluster mount requires a shared storage device that can be accessed by other
cluster mounts of the same file system. Writes to the shared device can be done concurrently from any host on
which the cluster file system is mounted. To be a cluster mount, a file system must be mounted using the
mount -o cluster option. See local mounted file system.
contiguous file A file in which data blocks are physically adjacent on the underlying media.
CVM The cluster functionality of VERITAS Volume Manager.
data block A block that contains the actual data belonging to files and directories.
data synchronous writes A form of synchronous I/O that writes the file data to disk before the write
returns, but only marks the inode for later update. If the file size changes, the inode will be written before the
write returns. In this mode, the file data is guaranteed to be on the disk before the write returns, but the
inode modification times may be lost if the system crashes.
defragmentation The process of reorganizing data on disk by making file data blocks physically adjacent to
reduce access times.
direct extent An extent that is referenced directly by an inode.
direct I/O An unbuffered form of I/O that bypasses the kernel’s buffering of data. With direct I/O, the file
system transfers data directly between the disk and the user-supplied buffer. See buffered I/O and
Unbuffered I/O.