Hitachi TrueCopy for z/OS (T1711-96009, June 2006)

TrueCopy for z/OS user guide 33
• Inflow control by RCU: If the RCU is not able to settle a recordset within the user-specified offloading
timer value, the RCU suspends all TC390A volume pairs and resets the channel-command-retry
condition to avoid hanging up the MCU.
HXRC. HXRC operations use a different cache sidefile than TC390A. Table 8 on page 33 also shows the
sidefile threshold values for HXRC operations and describes the actions that occur when each threshold is
reached. Disk arrays performing TC390A in combination with HXRC must have sufficient cache installed to
handle the increased sidefile activity. If a “sidefile puncture” condition occurs (HXRC sidefiles reach 10%
over threshold), the XRC session having the highest sidefile usage is terminated.
SIM reporting for sidefile conditions is disabled when mode 118 is OFF (Table 4
on page 20).
NOTE: Cache LUN XP operations may decrease the total amount of cache available for TC390A and
HXRC operations, but do not directly affect sidefile cache usage. Available cache is defined as the amount
of physical cache memory installed on the disk array minus any cache reserved for the Cache LUN XP
feature.
Graduated Delay Sidefile Management
The following figure shows the graduated delay process for TC390A sidefile management. When the
TC390A sidefile value reaches the high-water mark (threshold minus 20%), the
XP1024/XP128/XP12000/XP10000 begins command retry delay for host updates to TC390A M-VOLs
and reports a warning SIM to the host. As the amount of sidefile increases, the delay increases
incrementally as shown in the following figure. Use Mode 93 on the XP1024/XP128/XP12000/XP10000
SVP (refer to Table 4
on page 20) 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.
Table 8 Sidefile thresholds
Operation Threshold(s) Action(s)
TC390A High-water mark (HWM) = sidefile threshold –
20%
MCU (RCU) reaches HWM: command
retry to host (MCU), begin graduated
delay. Delay times can be adjusted using
mode 93 (see Table 4 on page 20).
Sidefile threshold = 30-70% of cache, default =
50%.
TC390A threshold can be adjusted from 30-70%
(in 10% increments) using TC390 through
Command View XP or XP Remote Web Console.
MCU (RCU) reaches threshold: command
retry to host (MCU), max delay time (500
or 100 ms). Delay time can be adjusted
using mode 93 (see Table 4 on page 20).
Puncture threshold = sidefile threshold + 10% MCU (RCU) reaches puncture: suspend
affected TC390A pairs due to sidefile
overflow condition.
HXRC
1
1. For more information on sidefile thresholds for HXRC operations, refer to ”HXRC Device Blocking and Load Balancing” on
page 212.
[XRC sidefile] / [avail cache] = 40%, 50%, 60%
XRC thresholds can be adjusted by using modes 85
and 86 (see Table 4 on page 20).
Threshold 1/2/3 = 30/40/50%, 40/50/60%, or
60/70/80%
Threshold 1 = command retry.
Threshold 2 = SCP message.
Threshold 3 = puncture condition.
Write Pending [write pending] / [avail cache - sidefile] = 70% Command retry.