HP 9000 Virtual Library System - Manual (Page 248)

L
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 virtual tape library. Software emulation of
a physical tape library is called a virtual tape library.
See also virtual tape library..
logical unit number
(LUN) An address used in the SCSI protocol to access a device within a target. In the case of the VLS,
a LUN is assigned to each virtual library and tape drive.
LUN mapping A mechanism of changing the LUN assignments for a specific host.
LUN masking An authorization process that makes a LUN available to some hosts and unavailable to other
hosts.
M
mean time until
data loss (MTDL) The average time until a component failure can be expected to cause data loss. This includes the
consideration that RAID redundancy can protect against data loss from the failure of a single
component.
media access
control (MAC)
address A low-level unique hardware identifier for every Ethernet port in the world that is physically stored
inside a network card or similar network interface. MAC addresses are assigned by the IEEE.
media server A computer whose purpose is to move or copy data from one location to another, such as from
network clients to tape cartridges in a library.
metadata The data in the first sectors of a disk drive that the system uses to identify virtual disk members.
mirroring The act of creating an exact copy or image of data.
N
node A server that contains the hardware and firmware required to run a virtual library system. This
refers to a hardware assembly containing a power supply, cooling fans, motherboard, expansion
boards, and internal hard drives to support the VLS system.
O
oversubscription A condition that exists when more virtual media storage is configured on a VLS than there is
physical storage available.
Because the VLS dynamically allocates storage space as user data is written, the VLS allows you
to allocate more storage for virtual media than is physically available.
R
RAID A RAID volume consists of more than one drive, but appears to the operating system to be a
single logical disk. RAID improves performance by disk striping, which involves partitioning each
drive's storage space into units. By placing data on multiple disks, I/O operations can overlap
in a balanced way, improving performance.
RAID1-level data
storage A RAID that consists of at least two drives that use mirroring (100 percent duplication of the
storage of data). There is no striping. Read performance is improved since either disk can be
read at the same time. Write performance is the same as for single disk storage.
RAID5-level data
storage A RAID that provides data striping at the byte level and also stripe error correction information.
RAID5 configurations can tolerate one drive failure. Even with a failed drive, the data in a RAID5
volume can still be accessed normally.
RAID6-level data
storage A RAID that provides data striping at the byte level and also stripe error correction information.
RAID6 configurations can tolerate two drive failures. Even with two failed drives, the data in a
RAID6 volume can still be accessed normally. RAID6 read performance is similar to RAID5, since
all drives can service read operations, but the write performance is lower than that of RAID5
because the parity data must be updated on multiple drives.
248 Glossary