Planning The Parallel Scsi Configuration; About Parallel Scsi Busses; Optimizing Throughput - HP StorageWorks 1/8 User's And Service Manual

• For SAS Autoloaders, install a SAS host bus adapter (HBA) with an external SAS connector that
supports multiple LUNs. Refer to the manuals for the host computer and the HBA for installation
information. See
• For Fibre Channel Tape Autoloaders, install an FC host bus adapter (HBA) or verify that you have
sufficient ports available on a compatible Fibre Channel switch. See
configuration" on page 30 for configuration requirements.
• Install application software and compatible drivers on the host computer. See the application
software manuals for installation and configuration information.
• Make sure multiple LUN support is enabled on the host computer. See
port" on page 18.

Planning the parallel SCSI configuration

If the host computer will have multiple parallel SCSI devices, you must decide how they will be
configured into one or more parallel SCSI busses.

About parallel SCSI busses

A parallel SCSI bus consists of the host bus adapter (HBA), the parallel SCSI devices, the parallel
SCSI cables, and the terminators. The HBA and devices are connected in a chain, with each device
connected to the next. The last device must have a SCSI terminator. Each device in the chain must
have a unique SCSI address (SCSI ID).
Complex devices, such as the Autoloader, assign sub-addresses, called logical unit numbers (LUNs),
to different parts of the device. The HBA and operating system must support multiple LUNs, also called
LUN scanning, for the application software to operate the Autoloader. HP Smart Array controllers,
most third-party RAID controllers, and many on-board SCSI controllers do not support multiple LUNs.
An HBA might have one or two channels, with each channel supporting one parallel SCSI bus. Check
to see how many channels the HBA has and what devices are already connected to the HBA. Some
devices, such as parallel SCSI disk drives, could be inside the server.
The devices on a parallel SCSI bus share bandwidth so be careful about which devices you put
together on a bus. Also, putting a single-ended (SE) SCSI device on the bus will slow all of the devices
on the bus down to SE speed. Check each device's interface specifications to see what kind of parallel
SCSI interface it has.

Optimizing throughput

If possible, put the Autoloader on its own parallel SCSI bus. This will give you the best performance
and easiest installation.
If a tape drive must share a parallel SCSI bus with one or more other devices, follow these guidelines
to plan your parallel SCSI busses for the highest performance:
• Do not put a tape drive on the same parallel SCSI bus as a disk drive because the system and
backup performance will be slow when data is written from the hard drive to tape or from tape
to the hard drive.
• Do not put a tape drive on the same parallel SCSI bus as a disk array because the disk and the
tape drive performance will be affected, most RAID controllers do not support multiple LUNs, and
the data on the disk array could become corrupted.
• Avoid putting an SE SCSI device on the same bus as a tape drive because the SE device will slow
the tape drive to SE speed and reduce the allowable cable length.
28 Installing the Tape Autoloader
Planning the SAS configuration" on page 29 for configuration requirements.
Planning the Fibre Channel
Multiple LUN sup-