Avago Technologies 3ware SAS 9750-16i4e - Manual (Page 312)

Appendix A. Glossary
300 3ware SATA+SAS RAID Controller Card Software User Guide, Version 10.2
• Striping. The process of breaking up files into smaller sizes and
distributing the data amongst two or more drives. Since smaller amounts
of data are written to multiple disk drives simultaneously, this results in
an increase in performance. Striping occurs in RAID 0, 5, 6, 10 and 50.
• Subunit. A logical unit of storage that is part of another unit. For
example, the mirrored pairs (RAID 1) in a RAID 10 unit are subunits of
the RAID 10 unit.
• Unit ID . A unique identifier for a specific unit in a system.
• Unit Number . The SCSI number, or channel number, of a particular unit.
• Unit . A logical unit of storage, which the operating system treats as a
single drive. A unit may consist of a single drive or several drives. Also
known as an array.
• Verify . A process that confirms the validity of the redundant data in a
redundant unit. For a RAID 1 and RAID 10 unit, a verify will compare the
data of one mirror with the other. For RAID 5, RAID 6, and RAID 50, a
verify will calculate RAID 5 parity and compare it to what is written on
the disk drive.
• VPort. The 3ware 9750 RAID controller has 127 addresses available to
assign to hard drives. These addresses are known as virtual port (vport)
IDs. By using vport IDs and expanders, one controller phy can connect to
multiple drives. This is in contrast to standard port connections which are
one-to-one physical connections.
• Wide Port . A SAS port can consist of one or more phys. When a SAS
port consists of one phy it is known as a narrow port, when it contains
multiple phys it is known as a wide port. The 3ware 9750 controllers has
multiple wide port connectors that contain 4 phys each. These phys can
function individually, in which case each phy has its own SAS address, or
the 4 phys can be banded together, in which case they share the same SAS
address. A 9750 wideport can have a bandwidth of up to 12.0 Gbps for
SAS 1.1 and 24 Gbps for SAS 2.0..
• WWN (World Wide Number). The unique worldwide 64-bit SAS address
assigned by the manufacturer to each SAS port and expander device in the
SAS domain. Many SAS drives have 2 ports and thus 2 WWNs.
• Write Cache. When write cache is enabled, data will be stored in
controller cache and drive cache before the data is committed to disk.
This allows the system to process multiple write commands at the same
time, thus improving performance