BA1001 - SCSI 2x1 LVD Switch
Overview
This switch allows you to share a SCSI device between two SCSI hosts. The switch
allows the device to be connected to both hosts simultaneously but access is controlled
by the SCSI Reserve/Release mechanism.
The SCSI Reserve/Release command allows a host to reserve the device for its
own use. Attempts to access from the other host are then rejected until the first
host releases the device. This has always been the sharing mechanism of choice
by device manufactures.
However, not all operating systems support SCSI Reserve/Release mechanism and
it is not possible to connect the SCSI busses of two hosts together.
This switch overcomes all these issues and effectively joins and isolates the
host SCSI busses.
The hosts access the device in the usual way, no additional software required.
If the device is currently being used by the other host, then this host receives
a benign not available, not ready or busy message.
Typically Applications
- Sharing NCTP/3950/3570 Timberline drives between multiple hosts dynamically
- Host fail-over protection for SCSI Raid or tape libraries
Instillation
The SCSI out connector is marked TAPE and should be attached the SCSI device.
The host computers are connected to HOST 1 and HOST 2. Each host will "see"
the SCSI device at its SCSI ID.
All SCSI connections are fast-wide differential.
Ensure the SCSI device connected to TAPE is terminated with a differential
terminator.
Ensure the SCSI device is set to SCSI ID 0, 1, 2 or 3.
In AS400 environment
For a new instillation it may be desirable to create the devices in OS400 for
each computer. Connect the drive directly and using STRSST. This can be done through
the switch for each host in turn. But ensure to vary-off the device in the other
host before proceeding.
Ensure that the drives in the hosts are varied off.
Connect the SCSI device to the switch and power on the device. Connect each
AS400 to the HOST connectors and switch the inputs. Power on the switch and vary
on on host. Check the device exists and then vary the device off at this host.
Repeat for the other host.
In NT/UNIX environments
Ensure the host's SCSI channel is dedicated to the switch only and there are
no other internal SCSI devices attached to the same bus.
This is important not only for correct operation but also ensures the maximum
throughput for the switched device.
Boots the host in turn, with the switch and tape device connected and powered.
This will allow the OS to create the necessary device drivers.
The switch may require a particular jumper setting depending upon the type
of host.
Front Panel LEDs
Red LED, Target Bus Error
Normally off. If this LED is on, SWITCH OFF the power and disconnect the device
cable. This indicates that there is an error with this device. Typically the terminator
is a single ended SCSI device or the SCSI cable is faulty.
Yellow LED, Term power Target
Normally on.
Green Led, Bus Free
Indicates when the device is in a bus free state. Normally when there is no
host activity or the host has disconnected for a period of time (space rewind
etc.)
Green LED, Host 1, 2 Busy
Indicates SCSI busy (activity) in the respective host
Green LED, Host 1, 2 Reserve
Shows which host has reserved the device.
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