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Inflow control of recordsets, Inflow control of, Recordsets – HP StorageWorks XP Remote Web Console Software User Manual

Page 31

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Hitachi TrueCopy for z/OS user guide

31

MCU power-off sequence is initiated, and also maintain sequence numbers in periods of low host

activities.

Figure 4

Selecting and settling TrueCopy Async recordsets at the RCU

Inflow control of recordsets

As described in the previous sections, both the MCU and RCU create sidefiles for storing TC390A

recordsets. Because the sidefiles occupy exclusive space in cache, both the MCU and RCU perform inflow

control to prevent an overload of the disk array’s cache resources. The XP12000/XP10000 uses the

following parameters (specified on the TC390 Async Option window, see ”

Asynchronous copy option

” on

page 108) for TC390A cache inflow control:

Sidefile Threshold = maximum cache % available for use by TC390A sidefiles.

Table 8

on page 32

shows the TC390A sidefile threshold values and describes the actions that occur when each threshold is

reached.
• The “high-water mark” (HWM), which is the sidefile threshold minus 20%, indicates when

graduated delay begins for TC390A volume pairs (see the following section). If SVP system option

mode 118 is ON, a warning SIM is also generated.

• The puncture threshold, which is the sidefile threshold plus 10%, indicates when the TC390A pairs

will be suspended due to sidefile overflow (see

CESTPATH

” on page 161).

• Inflow control by MCU: When the amount of MCU sidefile cache reaches the HWM, the MCU

responds to update I/Os from the host with state-change-pending (SCP) or channel-command-retry

requests and begins graduated delay.

• Inflow control by RCU: When the amount of RCU sidefile cache reaches the HWM, the RCU

responds with channel-command-retry requests to the RIO commands, which transfer the recordsets

from the MCU. The only recordset accepted by the RCU is the recordset with the sequence number

required to continue settling pending recordsets.

Offloading Timer = maximum time between TC390A recordset transfers.
• Inflow control by MCU: If the MCU is not able to send a recordset to the RCU within the

user-specified offloading timer value, the MCU suspends all TC390A pairs and resets the SCP

condition to avoid hanging up the system.

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