Dell EMC Solutions Enabler 9.2 SRDF Family CLI User Guide

SRDF/A write pacing extends the availability of SRDF/A by preventing conditions that result in cache overflow on both the R1 and R2 sides. Write pacing balances cache utilization by extending the host write I/O response time to prevent SRDF/A operational interruptions.

Group-level pacing

Group-level pacing controls the amount of cache used by SRDF/A. This prevents cache overflow on both the R1 and R2 sides, and helps the SRDF/A session to continue running.

Group-level pacing requires Enginuity 5876 or greater.

SRDF/A write pacing is not allowed on VASA SRDF groups.

HYPERMAX OS introduced enhanced group-level pacing. Enhanced group-level pacing paces host I/Os to the DSE transfer rate for an SRDF/A session. When DSE is activated for an SRDF/A session, host-issued write I/Os are throttled so their rate does not exceed the rate at which DSE can offload the SRDF/A session's cycle data.

Enhanced group-level pacing requires HYPERMAX OS on the R1 side. The R2 side can be running either HYPERMAX OS or Enginuity 5876.

Enhanced group-level pacing responds only to the spillover rate on the R1 side. It is not affected by spillover on the R2 side.

Device-level pacing

Device-level pacing is for SRDF/A solutions in which the SRDF/A R2 devices participate in TimeFinder copy sessions.

SRDF/A device-level write pacing addresses conditions that lead to cache overflow specifically due to TimeFinder/Snap and TimeFinder/Clone sessions on an R2 device running in asynchronous mode.

Device-level write pacing requires Enginuity version 5876 or higher on both arrays.

Either or both write pacing options can be enabled or disabled. Both write pacing options are compatible with each other and with other SRDF/A features including tunable cache utilization, Reserve Capacity, and MSC.

Enginuity version 5876.82.57 or higher includes a global write pacing statistics report.

Group-level and device-level write pacing can be activated and controlled individually or simultaneously at the group, device group, composite group, or file level on the R1 side.

Both methods have an autostart capability that automatically activates write pacing whenever an SRDF/A session becomes active. If an SRDF group has both group-level and device-level pacing configured to autostart, both are activated when the SRDF/A session becomes active.