Specifications

LUN affinity
For SCSI attachment, logical unit numbers (LUNs) have an affinity to SCSI ports,
independent of which hosts might be attached to the ports. If you attach multiple
hosts to a single SCSI port, each host has the exact same access to all the LUNs
available on that port.
Targets and LUNs
For SCSI attachment, each SCSI bus can attach a combined total of 16 initiators
and targets. Because at least one of these attachments must be a host initiator, that
leaves a maximum of 15 that can be targets. The ESS is capable of defining all 15
targets on each of its SCSI ports. Each can support up to 64 LUNs. The software in
many hosts is only capable of supporting 8 or 32 LUNs per target, but the
architecture allows for 64. Therefore, the ESS can support 960 LUNs per SCSI port
(15 targets x 64 LUNs = 960).
FlashCopy and PPRC restrictions
When you copy a source volume to a target volume with FlashCopy or PPRC and
you require concurrent read/write access of both volumes, the source and target
volumes should be on different host systems. A copy operation with the source and
target volume on the same host system creates a target volume with the same
identification as the source volume. The host system sees two identical volumes.
When the copy operation creates the same identification for the target volume as
for the source volumes, you are not able to distinguish one from the other.
Therefore, you might not be able to access the original data.
Note: You cannot create a host target on a single Novell NetWare host system. For
Novell NetWare, the target volume must be attached to a second Novell
NetWare host system.
The target volume and the source volume can be on the same host system for a
PPRC or FlashCopy operation only under the following conditions:
v For AIX, when the host system is using a logical volume manager (LVM) with
recreatevg command support.
v For AIX, Sun, and HP, when the host system is not using a logical volume
manager.
v For any host system, when the host system can distinguish between a source
and a target volume that have the same identification.
SCSI host system limitations
Table 6 shows the configuration limitations for the host systems. These limitations
can be caused by the device drivers, hardware, or different adapters that the host
systems support.
Table 6. Host system limitations
Host System
LUN
assignments
and limitations
per target Configuration notes
Compaq OpenVMS 0 - 7 None
Compaq Tru64 4.x 0 - 7 None
Compaq Tru64 5.x 0 - 15 None
Chapter 1. Introduction 11
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