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68 Chapter 2 Overview of CCI Operations
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.
HOST1
LDKC#
4Byte LDEV# LDKC# + 2Byte LDEV#
Inquiry
Command
d
c
e
2Byte LDEV#
CM
LDKC#
CM
LDKC#
USP V (64kLDEV*2)
Figure 2.37 Relation between LDEVs and Command Device on LDKC
c 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
d 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
e 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.