HP StorageWorks XP Remote Web Console Software - Manual (Page 24)

resources. The XP disk array uses the following parameters for TrueCopy for Mainframe
Asynchronous cache inflow control:
•
Sidefile Threshold = maximum cache % available for use by TrueCopy for Mainframe
Asynchronous sidefiles.
“Sidefile Thresholds” (page 24) shows the TrueCopy for Mainframe Asynchronous 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 TrueCopy for Mainframe Asynchronous pairs (see next section).
If 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
TrueCopy for Mainframe Asynchronous pairs will be suspended due to sidefile overflow.
◦ 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 (70%),
the RCU responds with channel-command-retry requests to the RIO commands. 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 TrueCopy for Mainframe Asynchronous 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 TrueCopy for Mainframe
Asynchronous pairs and resets the SCP condition to avoid hanging up the system.
◦ 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 TrueCopy for Mainframe Asynchronous
pairs and resets the channel-command-retry condition to avoid hanging up the MCU.
Compatible XRC and Concurrent Copy (CC): Compatible XRC and CC operations use a different
cache sidefile than TrueCopy for Mainframe Asynchronous.
“Sidefile Thresholds” (page 24) also
shows the sidefile threshold values for Compatible XRC and CC operations and describes the
actions that occur when each threshold is reached. Storage systems performing TrueCopy for
Mainframe Asynchronous in combination with Compatible XRC and/or CC must have sufficient
cache installed to handle the increased sidefile activity. If a sidefile puncture condition occurs
(Compatible XRC + CC sidefiles reach 10% over threshold), the CC session having the highest
sidefile usage is terminated (or XRC session if there is no CC session).
IMPORTANT: SIM reporting for sidefile conditions is disabled when mode 118 is OFF ( “XP Disk
Array Modes for TrueCopy for Mainframe” (page 12) ).
Cache Residency Manager operations may decrease the total amount of cache available for
TrueCopy for Mainframe Asynchronous, Compatible XRC, and CC operations but do not directly
affect sidefile cache usage. Available cache is defined as the amount of physical cache memory
installed on the storage system minus any cache reserved for the Cache Residency Manager feature.
Table 3 Sidefile Thresholds
Action(s) Threshold(s) Operation
MCU (RCU) reaches HWM: command
retry to host (MCU), begin graduated High-water mark (HWM) = sidefile
threshold – 20% TrueCopy for Mainframe
Asynchronous
delay. Delay times can be adjusted
using mode 93 (see
“XP Disk Array
24 About TrueCopy for Mainframe Operations