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

Page 31: Recordsets

When the top of each queue contains a valid entry (recordset), the RCU selects the entry that has the

earliest time-stamp value, and then settles this recordset.

The RCU repeats this process to select and settle TC390A recordsets.

The following figure illustrates recordset selection and settling at the RCU. In this example, the top of the

queue contains a valid entry: S1/T1. The RCU selects recordset S1/T1 to be settled because T1 is the

earliest time-stamp. When S1/T1 is removed from the MCU queue, recordset S2 becomes the top entry,

but it is empty. When recordset S2 arrives (and its time-stamp is later than T1 and earlier than T3), the

RCU selects S2/T2 as the next recordset to be settled. The recordset selected by the RCU is marked as

“host-dirty” and treated as formal data. The time-stamp value of that recordset is promoted to the

consistency time (C/T) of the group. The RCU settles the updated records in the recordset as follows:

•

If the corresponding track is in cache (track-hit), the updated records in the recordset are copied to the

existing cached track and the 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. The data is not physically moved.

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 and when an

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

XP128/XP1024/XP10000/XP12000 uses the following parameters (specified on the TC390 Async

Option window, see ”

” on page 102) for TC390A cache inflow control:

•

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

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

is reached.