PlatinumNAS Owner’s Manual
Performance
Performance is an important criterion on which a customer judges a RAID
controller. There are a number of popular benchmarking utilities that are available to
measure the I/O performance of a controller. Some of these utilities simulate specific real-life
applications and provide the user a score indicating the controller’s overall performance in
that niche. Others allow the user to specify tests with specific I/O characteristics and generate
throughput numbers corresponding to each specification. The nature of the tests a user may
wish to conduct on a controller depends on the application space in which that controller is
anticipated to be deployed.
Physical Drive
A single tangible drive is referred to as a physical drive.
Primary Storage
Main memory i.e., RAM is frequently referred to as primary storage.
RAID
Abbreviation of Redundant array of independent disks. It is a set of disk array
architectures that provides fault-tolerance and improved performance.
RAID Type
There are a number of RAID formats that are widely used. Some of the well-known
uni-level types are RAID 0, RAID 1, RAID 3, RAID 5 and RAID 6. The prevalent complex types
are RAID 10 and RAID 50. ,
RAID 0
RAID 0 utilizes simple striping, with the data being distributed across two or more
disks. No data redundancy is provided. The figure below illustrates a purely hypothetical
RAID 0 array comprised of three disks – disks A, B, and C – with four stripes – each uniquely
colored – across those disks.
Advantage:
Striping can improve the I/O throughput by allowing
concurrent I/O operations to be performed on multiple disks comprising the RAID 0 array.
However, this RAID type does not provide any data redundancy.
RAID 1
An array that uses a single pair of disks. Both disks in the pair contain the same
data It provides the best data protection but can’t improve system performance. And storage
space for the same data capacity should be double than in general cases. Hence storage cost
doubles. The capacity of RAID 1 will be the size of the smaller HDD, so we suggest you
connect HDDs of the same sizes to save HDD space.
Advantage:
RAID 1 ensures that if one
of the disks fails, its contents can be retrieved from the duplicate disk. Furthermore, a RAID
1 array can also improve the throughput of read operations by allowing separate reads to be
performed concurrently on the two disks.
RAID 5
A RAID 5 array is similar to a RAID 4 array in that, it utilizes a striped set of three
or more disks with parity of the strips (or chunks) comprising a stripe being assigned to the
disks in the set in a round robin fashion. The figure below illustrates an example of a RAID
5 array comprised of three disks – disks A, B and C. For instance, the strip on disk C marked
as P(1A,1B) contains the parity for the strips 1A and 1B. Similarly the strip on disk A marked
as P(2B,2C) contains the parity for the strips 2B and 2C.
Advantage:
RAID 5 ensures that if
one of the disks in the striped set fails, its contents can be extracted using the information on
the remaining functioning disks. It has a distinct advantage over RAID 4 when writing since
(unlike RAID 4 where the parity data is written to a single drive) the parity data is distributed
across all drives. Also, a RAID 5 array can improve the throughput of read operations by
allowing reads to be performed concurrently on multiple disks in the set.
D-Glossary
