1. epci164.exe Driver
2. STRIPE.TXT File Contents

STRIPE.TXT Driver File Contents (epci164.exe)

		      ATTO Striping Support on Windows NT
		      ---- -------- ------- -- ------- --


		       Striping support with Windows NT
		       -------- ------- ---- ------- --

NT does not support stripe groups on removable drives.  Another problem with
NT's implementation of striping is the fact that 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 64k, NT must send 16 requests down through the driver
hierarchy.  Finally, there is no provision in NT to vary the interleave - it
is fixed at 64k.  This may or may not be optimum for any given application.


			ATTO driver striping support
			---- ------ -------- -------

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 NT.  It is possible using the ATTO apporach 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 - NT, 95, OS/2, DOS, NetWare.

ATTO's driver supports striping at the miniport driver level in NT.  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 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.


			    Removable Drives
			    --------- ------

If the last drive in a stripe set is removable, the composite drive is reported
to the system as a removable drive.  Note that ALL members of a stripe set
MUST be exactly the same size.

Whenever any of the following error situations are encountered during the
processing of any request (striped or not), any further attempt to access that
drive or stripe set will generate a selection timeout error until a new 
bus scan is accomplished.

	. Selection Timeout
	. Check Condition / Power On Reset
	. Check Condition / Media Changed

Therefore, whenever the operator changes the media in a removable drive, a new
bus scan must be initiated.  One easy way to accomplish this is to run Disk
Manager from the Administrative Tools group.  Disk Administrator performs a
bus scan each time it starts up.

There are several restrictions for removable drives in Windows NT.

.	At least one SCSI disk drive must be present in the system at system
	startup time.  This is because NT will not load the SCSI disk class
	driver module at startup unless it sees at least one SCSI disk, and Disk
	Manager cannot load SCSI class drivers, even though it recognizes them
	during its bus scan.

.	NT 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.

.	In NT, 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 NT 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 NT 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.

.	NT 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.