Hitachi TrueCopy for IBM z/OS User and Reference Guide (T5211-96001, June 2007)

2-26 About TrueCopy for z/OS Operations
Hitachi Universal Storage Platform V TrueCopy for IBM z/OS User’s Guide
Graduated Delay Sidefile Management
Figure 2-4 shows the graduated delay process for TrueCopy for z/OS sidefile
management. When the sidefile value reaches the high-water mark (threshold
minus 20%), the USP V begins command retry delay for host updates to TCz
M-VOLs and reports a warning SIM to the host. As the amount of sidefile
increases, the delay increases incrementally as shown in Figure 2-4. Mode 93
on the USP V SVP (refer to Table 2-2) allows you to select the delay type (long
or short). This graduated delay methodology minimizes the potential for
sidefile overcommitment, while at the same time providing another level of
automation control.
Note: If there is a network problem, lack of bandwidth, or lack of sufficient
Fibre links, the sidefile will grow and the microcode will add delay to host I/O
until the sidefile goes below a certain level again. Disabling this function will
cause the pairs to suspend.
Important:
SIM reporting for sidefile conditions is enabled only when system
option mode 118 or 464 is ON (refer to Table 2-2). The reported SIM(s) when
system option mode 118 or 464 is ON, however, do not support a CLPR. When
this SIM is reported to the host, the SIM reference code is indicated as 490x-
yy ("x" is CU number, and "yy" is LDEV number). For further information on
the SIM reference code, please call the Hitachi Support Center.
You can disable the command retry delay for a limited number of critical
volumes using the special “No delay” parameter for the CESTPAIR TSO
command. When this parameter is set, the USP V will not delay host write I/Os
to the M-VOL until the sidefile amount reaches the puncture threshold
(threshold + 10%). This prevents performance degradation for critical volumes
and should be used only for a small number of volumes.