Appendix E - Glossary - Accusys ACS-9910 User Manual

Appendix E – Glossary
Logical Unit
Disk storage space on one or more physical drives that appears to the host computer as a
single drive.
LUN (Logical unit number)
The number assigned to a logical unit. Slices of a RAID are assigned (mapped to) LUNs by
which they appear to the host computer.
Mirroring
See Disk Mirroring.
Parity
Parity information is redundancy information calculated from actual data values. If any single
piece of data is lost, the data remaining and the parity information can be used together to
compute the lost data. Parity information can either be stored on a separate, dedicated drive, or
be mixed with the data across all the drives in the array.
RAID (Redundant Array of Independent / Inexpensive Disks)
A disk array in which part of the storage capacity is used to store redundant information about
user data stored on the remainder of the storage capacity. The redundant information enables
regeneration of user data in the event that one of the array member disks or the access path to
it fails. See Parity. Different RAID levels offer different data throughput speeds and fault
tolerance (data redundancy). RAID 0 does not feature redundant information but is nonetheless
considered a special type of RAID.
SCSI
Small Computer System Interface.
Slice
A partition of an array. See LUN.
Striping
See Disk Striping.
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