Avago Technologies 3ware SAS 9750-16i4e - Manual (Page 309)

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• Initialize. For 3ware SATA RAID controllers, initialize means to put the
redundant data on the drives of redundant units into a known state so that
data can be recovered in the event of a disk drive failure. For RAID 1 and
10, initialization copies the data from the lower port to the higher port.
For RAID 5, 6, and 50, initialization calculates the RAID 5 parity and
writes it to disk (background initialization). This is sometimes referred to
as resynching, and does not erase user data.
Note: If foreground
initialization is done before the operating system has loaded, zeroes are
written to all of the drives in the unit. This process, done through the
3ware BIOS, does erase existing data.
• Logical Units. This term is used in the 3ware CLI. It is usually shortened
to “units.” These are block devices presented to the operating system. A
logical unit can be a one-tier, two-tier, or three-tier arrangement. Single
logical units are examples of one-tier units. RAID 1, RAID 5, and RAID
6 are examples of two-tier units and as such will have sub-units. RAID 10
and RAID 50 are examples of three-tier units and as such will have sub-
sub-units.
• JBOD. An unconfigured single drive. The acronym is derived from “just
a bunch of disks.” Note that earlier versions of the 3ware RAID controller
exported JBODs to the OS. This is no longer supported. Individual drives
should be configured as Single Disks in order to be made available to the
OS.
• Migration. The process of changing the characteristics of a unit. The
change can be to expand the capacity of the unit (OCE), change the stripe
size of the unit, change the unit from redundant to non-redundant, change
the unit from non-redundant to redundant, and to change the unit from
one type of redundant unit to another type of redundant unit (for example
RAID 1 to RAID 5).
• Mirrored disk array (unit). A pair of drives on which the same data is
written, so that each provides a backup for the other. If one drive fails, the
data is preserved on the paired drive. Mirrored disk units include RAID 1
and RAID 10.
• NCQ (Native Command Queuing). See “Queuing”
• Non-redundant units. A disk array (unit) without fault tolerance
(RAID 0 or single disk.).
• OCE (Online Capacity Expansion). The process of increasing the size of
an existing RAID unit without having to create a new unit. See also
migration.
• Parity. Information that the controller calculates using an exclusive OR
(XOR) algorithm and writes to the disk drives in RAID 5, RAID 6, and
RAID 50 units. This data can be used with the remaining user data to
recover the lost data if a disk drive fails.
• PCB . Printed circuit board.