Avago Technologies MegaRAID SAS 9240-4i - Manual (Page 91)

LSI Corporation
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6Gb/s MegaRAID SAS RAID Controllers User Guide
August 2013
S
SAS Acronym for Serial Attached SCSI. A serial, point-to-point, enterprise-level device
interface that leverages the proven SCSI protocol set. The SAS interface provides
improved performance, simplified cabling, smaller connections, lower pin count,
and lower power requirements when compared to parallel SCSI. SAS controllers
leverage a common electrical and physical connection interface that is
compatible with Serial ATA.
The SAS controllers support the ANSI Serial Attached SCSI Standard, Version 2.0. In
addition, the controller supports the Serial ATA III (SATA III) protocol defined by the
Serial ATA Specification, Version 3.0. Supporting both the SAS interface and the
SATA III interface, the SAS controller is a versatile controller that provides the
backbone of both server and high-end workstation environments. Each port on
the SAS RAID controller supports SAS devices, SATA devices, or both.
SAS device Any device that conforms to the SAS standard and is attached to the SAS bus by a
SAS cable. This includes SAS RAID controllers (host adapters) and SAS peripherals.
SATA Acronym for Serial Advanced Technology Attachment. A physical storage
interface standard, SATA is a serial link that provides point-to-point connections
between devices. The thinner serial cables allow for better airflow within the
system and permit smaller chassis designs.
SMP Acronym for Serial Management Protocol. SMP communicates topology
management information directly with an attached SAS expander device. Each
PHY on the controller can function as an SMP initiator.
SSP Acronym for Serial SCSI Protocol. SSP enables communication with other SAS
devices. Each PHY on the SAS controller can function as an SSP initiator or an
SSP target.
STP Acronym for Serial Tunneling Protocol. STP enables communication with a SATA
device through an attached expander. Each PHY on the SAS controller can
function as an STP initiator.
strip The portion of a stripe that resides on a single drive.
stripe size The total drive space consumed by a stripe not including a parity drive. For
example, if a stripe contains 64 KB of drive space and has 16 KB of data residing on
each drive, the stripe size is 64 KB and the strip size is 16 KB.
A larger stripe size produces improved read performance, especially if most of the
reads are sequential. For mostly random reads, select a smaller stripe size.
striping Drive striping writes data across two or more drives. Each stripe spans two or more
drives but consumes only a portion of each drive. Each drive, therefore, may have
several stripes. The amount of space consumed by a stripe is the same on each
drive that is included in the stripe. The portion of a stripe that resides on a single
drive is a strip, also known as a stripe element. Striping by itself does not provide
data redundancy; striping in combination with parity provides data redundancy.
strip size The drive space consumed by a strip. For example, if a stripe size contains 64 KB of
drive space and has 16 KB of data residing on each drive, the stripe size is 64 KB
and the strip size is 16 KB. The stripe depth is four (four drives in the stripe). You
can specify stripe sizes of 8 KB, 16 KB, 32 KB, 64 KB, 128 KB, 256 KB, 512 KB, or 1 MB.
RAID 0, 1, and 10 configurations for MegaRAID SAS 9240 RAID controllers are
limited to 16 drives and 64K stripe size. To exceed these limitations, you can plug
in a new MegaRAID SAS 9260 RAID controller or a a new MegaRAID SAS 9280
RAID controller. The MegaRAID Storage Manager utility recognizes and imports
the existing array with no reconfiguration required.