ATTO Striping Support
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Striping support with Windows NT, 2000, and XP
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Windows provides a disk striping mechanism that is implemented as filter driver.
There are several short comings to the Windows striping design.
1. Windows does not support stripe groups on removable drives.
2. There is no mechanism for the upper-level drivers to pass scatter/gather
tables down to the low level SCSI miniport driver. Therefore, the upper
level striping driver must break I/O requests up into smaller requests
that don't cross interleave boundaries.
For example, to satisfy a 1 megabyte I/O request to a pair of striped drives
with an interleave of 64KB, Windows must send 16 requests down through the driver
hierarchy.
3. There is no provision in Windows to vary the interleave - it is fixed at 64KB.
This may or may not be optimum for any given application.
4. Windows striping is only available in Windows. You cannot boot off a Windows
stripe group and it is not accesible in other Operating Systems.
ATTO driver striping support
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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:
1. Support of removable devices.
2. Optimize 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.
3. The ATTO striping provides for an interleave size from 2KB to 512KB.
4. An ATTO stripe group is recognized under BIOS and DOS environments. Therefore,
the boot drive can be a stripe group.
ATTO drivers support striping in a consistent manner for all operating systems.
Using ATTO's drivers, striping is accomplished by combining drives rather than
partitions, as in Windows. It is possible using the ATTO approach to boot the
system off of a striped set of drives. Furthermore, with a system configured
using ATTO's striping and multiple operating systems, all the operating systems
will be able to access the striped drives - Windows and DOS.
ATTO's driver supports striping at the miniport driver level in Windows. It does
so by detecting composite drives during the initial power-on bus scan. During
this scan, composite drives are detected and reported to the system only on the
last target ID of the stripe group. The miniport driver intercepts any SCSI
command sent to that composite drive reported on the highest ID and either
emulates the command, sends it to whatever drives in the stripe group are
required to satisfy the request, or rejects it as an illegal command. Any
command sent to one of the other drives in the stripe set is rejected with
a SCSI Selection Timeout error.
SCSI Inquiry and Read Capacity commands are emulated. Inquiry data is
fabricated to indicate a manufacturer ID of "ATTO" and a device ID of whatever
stripe group name was assigned when the group was created. Read/write/verify
requests are sent to the drives required to satisfy the request based on the
disk address range involved. Commands such as Test Unit Ready and Prevent/Allow
media removal are sent to all drives in the group. When an error occurs on any
or all drives in a stripe set, the first error which is detected is returned
with the command.
Stripe Interleave
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The stripe interleave defines how many logical blocks are used from one drive
in the stripe before the next drive's blocks are used. An interleave size of
64KB (default size) indicates that 64KB of data will come from one drive and
the next 64KB comes from the next drive. Therefore, performance optimization
attained with striping will only occur when the read or write command is
requesting more than 64KB of data. The size of the stripe interleave should be
matched to the average size of the read and write commands.
ATTO striping provides interleave sizes from 2KB to 512KB and the default size
is 64KB. The optimum interleave size is best determined by trial and error. An
interleave size should be chosen and then tested via a benchmark program or by
actual tests of the system.
NOTE: ATTO drivers prior to version 1.68 did not support an interleave size
greater than 64KB. If a stripe group with an interleave size greated than 64KB
is run under a driver whose version is before 1.68, the stripe group will be
inaccessible. That driver will report that members are missing from the stripe
group. Do not "repair" the stripe group with the 'RAIDUTIL.EXE" program or
all data will be lost. The stripe group can only be accessed with a driver
whose version is 1.68 or greater.
Removable Drives
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There are several restrictions for removable drives in Windows NT, 2000, and XP:
. Windows will only assign drive letters at system startup time. Therefore,
if no drive is present at a given SCSI Bus/ID combination at system
startup time, and a new bus scan is initiated after a drive becomes
available at such Bus/ID combination, no drive letter will be assigned
to that drive, even though Disk Manager will report on partitions
on the drive. (It is possible for a special application program to
assign a drive letter to such drives but no such application is
currently available.)
Most removable media drives will report their presence during any bus
scan as long as they are powered up even without media present. There
are, however, some pseudo-removable drives which do not report their
presence unless they are spun up.
. It is not possible to assign more than one drive letter to any
removable drive. Therefore, it is not possible to create multiple
partitions on any removable drive. This also applies to composite
removable striped drives.
. Once Windows sees a drive at a particular bus/ID combination, Disk Manager
will always report that drive as being there. So if, for example,
two removable drives have independent media installed during a
particular bus scan and on a subsequent scan the drives contain
striped media, both drives will show up in Disk Manager's scan. In
this case, Disk Manager will indicate that Configuration Information
is not available for the first drive but will indicate the appropriate
information for the stripe set on the second drive. There will also be
other warning messages during the bus scan, to which the user should
press the Ignore button.
. The Windows port driver does not re-scan device ID's it has seen on previous
bus scans. Therefore, once a particular ID has been associated with a
particular device type, changes in the device at that particular ID
will not take effect, for example, changing a disk for a tape unit.
. Windows only scans for LUNs (Logical Unit Numbers) on the bus scan where
that target ID first appears.
. Drive letter assignments are static - they reference a particular
DRIVE, not the media installed. Therefore, if the system remembers
pathnames to files on removable drives and the media is changed, any
such file may or may not be present and if present, may not reference
the desired file.
The ATTO striping logic has several mechanisms built in to provide maximum
configuration of removable drives.
. The ATTO striping code will report all removable drives to Windows.
Therefore, all removable drives will have a drive letter assigned. This
occurs 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 dircet
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.
Download Driver Pack
After your driver has been downloaded, follow these simple steps to install it.
Expand the archive file (if the download file is in zip or rar format).
If the expanded file has an .exe extension, double click it and follow the installation instructions.
Otherwise, open Device Manager by right-clicking the Start menu and selecting Device Manager.
Find the device and model you want to update in the device list.
Double-click on it to open the Properties dialog box.
From the Properties dialog box, select the Driver tab.
Click the Update Driver button, then follow the instructions.
Very important: You must reboot your system to ensure that any driver updates have taken effect.
For more help, visit our Driver Support section for step-by-step videos on how to install drivers for every file type.