HP StorageWorks XP Remote Web Console Software - Manual (Page 23)

Figure 3 Selecting and Settling XP Continuous Access Asynchronous Recordsets at the RCU
* Since the record set has not yet arrived at the RCU, S2 does not have a time stamp now.
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 pair status changes and when an
MCU power-off sequence is initiated, and also maintain sequence numbers in periods of low-host
activities.
Inflow Control of Recordsets
As described in the previous sections, both the MCU and RCU create sidefiles for storing XP
Continuous Access (and TrueCopy for Mainframe) Asynchronous recordsets. Since the sidefiles
occupy exclusive space in a cache, both the MCU and RCU perform inflow control to prevent an
overload of the storage system’s cache resources. The storage systems use the following parameters
for XP Continuous Access Asynchronous cache inflow control that you can modify as needed:
•
Pending Update Data Rate (%): sidefile (XP Continuous Access) threshold = maximum cache
% available for use by XP Continuous Access Asynchronous sidefiles.
•
I/O Delay Start (%): the threshold, which is the maximum amount of cache for starting the I/O
inflow control.
•
I/O Delay Increase (%): the threshold, which is the maximum amount of cache for starting to
strengthen control over the I/O inflow.
Inflow Control by MCU. When the amount of MCU sidefile cache reaches the user-specified threshold
(I/O delay start), the storage system’s I/O response is delayed. When the amount of MCU sidefile
cache reaches the user-specified threshold (I/O delay increase), the storage system's I/O delay
starts to increase. If the MCU is not able to send a recordset to the RCU within the user-specified
offloading timer value due to the condition of the amount of MCU sidefile cache exceeding the
sidefile threshold continuously, the MCU suspends all affected XP Continuous Access Asynchronous
pairs and resets the SCP condition to avoid hanging up the system.
Inflow Control by RCU. When the amount of RCU sidefile cache reaches the threshold (pending
update data rate) (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 the pending recordsets. If the RCU is not able to settle a recordset
XP Continuous Access Asynchronous Recordset Operations 23