Specifications

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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 Level 0
RAID Level 0 is commonly used when performance is
more important than data-protection.
RAID Level 0, also called striping, is accomplished by
mapping data across several disk drives. A single,
larger drive is created from several smaller ones. Data
is stored onto the physical drives in consecutive
“stripes,” defined by the interleave setting in the RAID
application. Files that are larger than the interleave
size are distributed sequentially across the disk drives
in the array. Because data is spread across several
drives, the actual throughput is a function of the
aggregate performance of all the drives in the stripe
group instead of just a single drive. Throughput is
equal to the number of drives times the speed of the
slowest drive in the stripe set.
You should strictly follow a backup policy to protect
data stored on RAID 0 volumes.
ATTO ExpressRAID Advantages
ATTO provides a disk striping method that is
implemented at the HBA driver level. The support
exists in the Windows driver, the BIOS driver and the
DOS driver.
The ATTO disk striping provides the following
features:
❖ Supports removable devices
Removable Drives report their presence during any
bus scan as long as they are powered up, even without
media present. Some pseudo-removable drives,
however, do not report their presence unless they are
spun up. Once Windows sees a drive at a particular
bus/ID combination, Disk Manager will always report
that drive as being there.
The ATTO striping code will report all removable
drives to Windows so that all removable drives will
have a drive letter assigned, even when a stripe set is
in the removable drives.
The ATTO striping driver will intercept I/O to any
drive that is a member of an ATTO stripe group. If the
drive is the primary stripe member then the I/O will be
performed against the stripe group. If the drive is not
the primary and it is a removable drive, the ATTO
stripe driver will return an error indicating MEDIA not
available. This mechanism retains the drive mapping
assigned by the initial scan. If the removable media is
replaced with a non-striped set of media the system
will be able to have direct access to the media. The
ATTO striping driver will recognize the fact that media
has changed in removable drives.The driver will then
institute a rescan of all removable drives that it
controls. Any changes to primary drives and stripe
groups will be recorded in the driver. The
reconfiguration of the removable drives is dynamic
and does not require Disk Administrator to be run.
❖ Optimizes SCSI requests.
The maximum number of SCSI I/O requests generated
is given by the number of disks in the stripe group
since the HBA driver has access to the scatter gather
information.
For example, to satisfy a 1 megabyte I/O request to a
pair of striped drives with an interleave of 64KB, the
ATTO driver will generate 2 SCSI requests.