disk mirroring A technique in which data is written to two duplicate disks simultaneously.
Mirroring provides data protection in the case of disk failure, because da ta is
constantly updated to both disks. This way if one of the hard drives fails, the
system can instantly switch to the other disk without any loss of data or service.
See also RAID 1-level data storage and failover protection.
disk striping The process of dividing a body of data into blocks and spreading the data
blocks across several par titions on several disks.
See also RAID.
disk-to-disk
backup
Typically refers to backing up data on disks rather than on tape. Disk-to-disk
backup systems provide a very fast single file restore capability compared with
disk-to-tape backup.
See also data restore and virtual tape.
disk-to-disk-to-
tape bac kup
Archiving in which data is initially c opied to backup storage on a disk-based
storage system, such as a VLS, and then periodically copied again to a tape
storage sy stem.
See also data migration.
dual port virtual
devices
Virtual devices (for example, the two host or device ports on each FC card in
the node) with connectivity to two ports so that the device can be connected to
more than one input or output.
dynamic disk
filesystem
A finely-tuned filesystem d eveloped to handle large block I/O typical of
a streaming backup/restore environment. This filesystem is optimized for
sequential access and very large file sizes.
extent The minimum amount of disk space allocated for writing by the VLS dynamic
disk filesystem. A smaller extent reduces wasted disk space, but decreases
restore performance. The VLS extent size is 32MB.
See also data restor e.
failover protection A backup operational mode in which the functions of a system component (such
as a hard drive or power supply) are assumed by secondary system components
when the p rimary component becom es un available through either failure or
scheduled down time.
Fibre Channel (FC ) A technology for transmitting data between computer devices at data rates
of up to 1 or 2 GB/second. FC is especially suited for connecting computer
servers to shared storage devices.
file AVLSfi le is a virtual cartridge.
Firesafe The holding area for virtual media that is not assigned to a virtual library. Data
cannot be restored from virtual med ia located in the Firesafe until the m e dia is
moved into a library.
hot plug The ability to add and remove devices to an appliance while the appliance is
running and have the operating system automatically recognize the change.
infrastruc ture The physical hardware used to interc onnect computers. Infrastructure also
includes the software used to send, receive, and manage the signals that are
transmitted.
initiator Media (host) server that runs the backup/restore application that p asses
commands and data bet ween the net work and the VLS.
inputs/outputs per
second
A measure of performance for a host-attached storage device or RAID controller.
library A storage device that handles multiple units of media and provides one or
more drives for reading and writing them, such as a physical tape library and
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Glossary
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