AdvFS Guide to File System Administration: Glossary

Glossary

/etc/fdmns directory: A directory that defines the file domains by providing a subdirectory for each file domain created on the system.
/etc/fstab file: A file that identifies filesets that are to be mounted at system reboot.
balance: To even the distribution of files between volumes of a file domain.
bitfile metadata table: See BMT.
block: A 512-byte unit of disk storage.
BMT: An array of 8-kilobyte pages, each with a header and an array of mcells. A BMT contains all metadata for all files with storage on a volume.
buffer cache: The area of memory that contains the blocks of data waiting to be written to disk.
checksum: See exclusive-or (XOR).
clone fileset: A read-only copy of a fileset that is created to capture fileset data at a particular time. The contents of the clone fileset can be backed up while the original fileset remains available to users.
contiguous: Storage that is physically adjacent on a disk volume.
defragment: To make files and free space in a file domain more contiguous.
dirty: Data that has been written by the application, but the file system has cached it in memory so it has not yet been written to disk.
domain panic: A condition that prevents further access to the file domain but allows the filesets in the file domain to be unmounted. AdvFS initiates a domain panic when a log or metadata write error occurs.
exclusive-or (XOR): Blocks created during tape backup for error recovery.
extent: One or more contiguous blocks on disk. Contiguous in this context means physically adjacent on a volume.
file domain: A named pool of storage that contains one or more volumes. Each file domain must have at least one fileset.
file domain identifier: A set of numbers that identify the file domain to the system.
file extent: See extent.
fileset: A hierarchy of directory and file names. It represents a mountable portion of the directory hierarchy of the AdvFS file system.
fileset quota: A quota that limits the amount of disk storage that a fileset can consume or the number of files a fileset can contain.
frag file: A file that allocates storage for files that are less than 8-kB in size (one page). Using fragments reduces the amount of wasted disk space.
file fragment: Created when a file uses only part of the last page (less than 8 kB) of file storage allocated or has a total size of less than 8 kB.
grace period: The period of time a quota's soft limit can be exceeded as long as the hard limit is not exceeded.
GUI: A graphical user interface.
hard limit: The quota limit for disk block usage or number of files that cannot be exceeded.
HSM: The POLYCENTER Hierarchical Storage Manager (Layered Product). HSM provides large amounts of tertiary storage for systems where speed of access is not important.
inode: An identifier for a UFS file that is like an AdvFS file domain tag.
kernel: The portion of an operating system that controls process scheduling and system resources such as virtual memory and storage devices.
Logical Storage Manager: See LSM.
LSM: The Logical Storage Manager (Layered Product). LSM is a volume management system that shadows volumes and provides volume-level striping.
metadata: File structure information such as file attributes, extent maps, and fileset attributes.
migrate: To move files from one volume to another within a file domain.
miscellaneous metadata bitfile: Maps areas of the volume that does not represent AdvFS metadata, such as the disk label and boot blocks.
NetWorker: The POLYCENTER NetWorker Save and Restore Solution. NetWorker provides scheduled, online automated back up.
page: An allocation of 8 kB of contiguous disk space (16 blocks).
product authorization key (PAK): License to access Digital Equipment Corporation software.
quota file: A file that keeps track of number of files, disk block usage, and grace period per user ID or per group ID. Fileset quota information is stored within the fileset.
root tag directory: Defines the location of all filesets in a file domain. Each file domain has one.
saveset: A collection of blocks created to save AdvFS backup information.
soft limit: The quota value beyond which disk block usage or number of files is allowed only during the grace period.
storage bitmap: Tracks free and allocated disk space. Each volume in a file domain contains one.
stripe: Allocates successive sections of files across successive volumes in a file domain.
transaction log: The log that records changes to metadata before the changes are written to disk. At regular intervals the changes in the transaction log are written to disk. The log is circular and is eventually overwritten.
trashcan: The directory that contains the most recently deleted files from an attached directory. The trashcan directory is set up by each user for user files.
volume: Anything that behaves like a UNIX block device. This can be a disk, disk partition, or logical volume.
write-ahead logging: The process where the modifications to the file-structure information are completely written to a transaction log before the actual changes are written to disk. This process is used to ensure file-system consistency in the event of a system failure.
XOR: See exclusive-or (XOR).