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ATTO Technology ExpressRAID for Macintosh
1 RAID Overview
Originally Redundant Array of Inexpensive Disks, now Redundant Array of Independent Drives, RAID is a
storage system using multiple disk drives. ATTO ExpressRAID creates virtual disk arrays on physical drives to
increase capacity and performance.
RAID (Redundant Array of Independent Disks) is a
storage system using multiple disk drives to increase
capacity and performance.
Large amounts of data can be supported over many
smaller drives when the drives are combined into one
large “virtual” drive. Management is easier because,
instead of several drives to consider when deploying
data as in a JBOD (Just a Bunch of Disks)
configuration, the system only has one address or LUN
on a storage bus or network.
RAID overlaps disk seeks, minimizing aggregate seek
time delays for the storage group as a whole. Data are
written in equal, short operations to each member of
the RAID group in turn so that when the first member
of a group begins writing to disk, the second member
is available to take data. This continues until the last
member of a group is writing to disk, and the first
member of a group is ready for data.
RAID also takes advantage of the Macintosh® OS
ability to create partitions and volumes.
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A logical partition is a separate portion of a
disk space used to allow multiple storage
volumes to coexist on a single disk drive.
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A volume is a quantity of storage composed
of one or more partitions residing on one or
more physical drives. A standard volume
creates a partition on a single drive.
RAID Level 0
RAID Level 0 is commonly used when performance is
more important than data protection. RAID Level 0, or
striping, achieves higher I/O performance by breaking
data into smaller units (volumes), then writing the data
to separate physical drives. These striped volumes can
then be read from the separate, physical drives, and re-
assembled into the actual data. You must have at least
two physical drives to create a striped volume. You
should strictly follow a backup policy to protect data
stored on RAID 0 volumes.
RAID Level 1
Disk RAID Level 1 (mirroring) ensures the security of
data by writing data simultaneously to two or more
drives. This application is for users with critical data,
which cannot be lost or corrupted due to the failure of
a single drive. With mirroring, users are protected from
loss of data because Data are stored in two or more
places. If a drive does fail, valuable data will not be
lost.
ATTO Recommendations
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Although RAID 0 volumes can be created
among different types and models of drives,
use similar types/models to ensure access
time will be equal to the average access time
of a single drive rather than the access time
of the slowest drive.
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For maximum performance, use a dual
channel host adapter with drives equally
distributed across busses.
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Use RAID 0 in environments that demand
high I/O rates such as video production and
editing, image editing and prepress.
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Since RAID 0 does not provide fault
tolerance, establish a backup policy to
protect data stored on RAID 0 volumes.
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ATTO ExpressRAID is designed to work
with any SCSI Manager 4.3 compatible
SCSI bus, but it has been optimized for use
with ATTO ExpressPCI SCSI-3 and Fibre
Channel host adapters.
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For the absolute highest performance using
SCSI, connect each of the drives to be
striped to a separate ATTO ExpressPCI
SCSI-3 host adapter. Multiple host adapters
increase performance by allowing data to be
transferred to all striped drives
simultaneously.
