Logical Dkc Per 64K Ldevs; Figure 2.37 Relation Between Ldevs And Command Device On Ldkc - Hitachi TAGMASTORE MK-90RD011-25 User Manual

2.8.8

Logical DKC per 64K LDEVs

The Universal Storage Platform V/VM controller manages internal LDEV numbers as a four-
byte data type in order to support over 64K LDEVs. Because the LDEV number for the host
interface is defined as two-byte data type, the USP V/VM implements the concept of the
logical DKC (LDKC) in order to maintain the compatibility of this host interface and to make
operation possible for over 64K LDEVs without changing the host interface.
LDKC#
LDKC# +

Figure 2.37 Relation between LDEVs and Command Device on LDKC

Converting to LDKC# and 2-byte LDEV: returns the LDEV number to the host by converting
from 4-byte LDEV# to LDKC# and 2-byte LDEV#.
LDKC# (0 or 1 for 128K LDEVs) = internal DKC LDEV# / 64K
LDEV# for the Host = internal DKC LDEV# % 64K
Converting to 4-byte LDEV: converts as internal LDEV# from LDKC# and 2-byte LDEV# to
4-byte LDEV#.
internal DKC LDEV# = 64K * LDKC# (0 or 1 for 128K LDEVs) + LDEV# from the host
Filtering to 2-byte LDEV: returns 2-byte LDEV# to the host by filtering 4-byte LDEV# via
the command device.
LDEV# for the host = internal DKC LDEV# - 64K * LDKC# (0 or 1 for 128K LDEVs)
If "0 ≤ LDEV# for the host < 64k", then returns LDEV# for the host, else returns NO LDEV.
Restrictions:
For TrueCopy Async, you cannot create a CT group across LDKC.
For ShadowImage and COW Snapshot, you cannot create a paired-volume across LDKC.
You must configure LUSE/POOL/JNL using multiple LDEVs within the same LDKC.
68 Chapter 2 Overview of CCI Operations
HOST1
Inquiry
2Byte LDEV#
2Byte LDEV#
USP V (64kLDEV*2)
Command
CM
CM
LDKC#
LDKC#
4Byte LDEV#