Portable Media Storage User Manual

RAIDBank5 Owner’s Manual

Read Ahead Cache Motivated by the principle of “spatial locality”, many RAID controllers

read blocks of data from secondary storage ahead of time, i.e., before an application actually

requests those blocks. The number of data blocks that are read ahead of time is typically

governed by some heuristic that observes the pattern of requests. The read-ahead technique

is particularly efficient when the spatial distribution of an application’s requests follows a

sequential pattern.

Read Through Cache Using this methodology, a read operation not only reads data from

secondary storage into system memory but also places the data into the cache such that future

need for the same data can be addressed expeditiously by directing a read operation for that

data into the cache only.

RAID Rebuild When a RAID array enters into a degraded mode, it is advisable to rebuild the

array and return it to its original configuration (in terms of the number and state of working

disks) to ensure against operation in degraded mode

SATA Acronym for “Serial ATA”. A hard disk drive interface standard developed to enhance

connectivity and speed over the IDE, or Parallel ATA disk interface. Current generation SATAII

supports speeds up to 300MB/S.

Stripe A stripe is a logical space that spans across multiple hard disks with each constituent

hard disk contributing equal strips (or chunks) of space to the stripe. In the figure below,

strips 1, 2, and 3 from hard disk 1, 2, and 3 respectively comprise a (purple colored) stripe.

Synonym: major stripe

Stripe Set A stripe set is a set of stripes that spans across multiple hard disks. In the figure

below, the displayed stripe set has 4 stripes, with strip number 1 comprised of the purple

strips 1A, 1B and 1C. Stripe number 2 is comprised of the green strips 2A, 2B and 2C etc.

Stripe Size This is the size of the strips that constitute each stripe. This term is a misnomer –

though prevalent – since it should appropriately be called strip size or chunk size.

TCP/IP This is an acronym for “Transmission Control Protocol/Internet Protocol”. It is

comprised of two parts TCP and IP. The former, i.e., TCP is a peer-to-peer connection oriented

protocol that guarantees the delivery of data packets in the correct sequence between two

peers. The latter, i.e., IP is the protocol that defines and governs addressing, fragmentation,

reassembly and time-to-live parameters for packets.

Universal Serial Bus (USB) is a specification created in 1996 by a consortium of companies

led by Intel to simplify the connection between host computer and peripheral devices. The

original USB 1.x specification was capable of 12 Mbit/sec. USB 2.0 is the most common port

at time of publication, and is capable of 480Mbit/sec gross bandwidth. USB 3.0 was ratified

in November of 2008, and is capable of 5Gbit/sec gross bandwidth.

Volume Set A volume set is a concatenation of storage elements that may be RAID arrays,

JBODs, or simply areas of disks that are not part of RAID arrays.

C-Glossary