Types Of Recordsets; Inflow Control Of Recordsets; Selecting And Settling Continuous Access Xp Async Recordsets At The Rcu - HP StorageWorks XP12000 User Manual

recordset the RCU selects is marked as "host-dirty" and treated as formal data. The RCU settles the
updated records in the recordset as follows:
• If the corresponding track is in cache (track-hit), updated records in the recordset are copied to
the existing cached track, and cache space for the sidefile is released.
• If the corresponding track is not in cache (track-miss), the RCU changes the cache designation
of the sidefile to formal data. Data is not physically moved.
Figure 3 Selecting and settling Continuous Access XP Async recordsets at the RCU

Types of recordsets

In addition to host update recordsets, the MCU passes control information to the RCU in special
non-update recordsets. These special recordsets indicate when volume pair status changes, indicate when
an MCU power-off sequence is initiated, and maintain sequence numbers in periods of low host activities.
Inflow control of recordsets
As described in previous sections, both the MCU and RCU create sidefiles for storing Continuous Access
XP Asynchronous recordsets. Because 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 array uses certain
parameters for Continuous Access XP Asynchronous cache inflow control. Use the Continuous Access XP
Async Option pane to modify the following parameters (see
• Pending Update Data Rate (%): Sidefile threshold = maximum cache % available for use by
Continuous Access XP Asynchronous sidefiles.
• Offloading Timer (sec.): Maximum time between Continuous Access XP Async recordset transfers.
• I/O Delay Start (%): Maximum amount of cache for starting I/O inflow control.
• I/O Delay Increase (%): Maximum amount of cache for starting to strengthen control over I/O
inflow.
Inflow control by MCU
When the amount of MCU sidefile cache reaches the user-specified threshold (pending update data
rate) (I/O delay start), the array's I/O response is delayed. When the amount of MCU sidefile cache
reaches the user-specified threshold (I/O delay increase), the array's I/O delay starts increasing. If the
MCU cannot send a recordset to the RCU within the user-specified offloading timer value because the
amount of MCU sidefile cache exceeded the sidefile threshold continuously, the MCU suspends all
affected Continuous Access XP Asynchronous volume pairs and resets the State Change Pending (SCP)
condition to avoid hanging up the system.
Asynchronous copy option):
Continuous Access XP user guide
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