VMAX cache is a globally shared resources, all applications on an array compete for cache slots. In case one cache unfriendly application might significantly impact the performance of other applications that have a higher hit rate. This might happen when a highly random cache unfriendly application recycles cache slots that were being used by a tier one application with high locality of reference. The latest versions of VMAX Enginuity allow Dynamic Cache Partitioning, a configurable and powerful way of segregating cache. This article indicates the description of DCP functionalities and how to configure DCP through Solutions Enabler command. 

The best uses for Dynamic Cache Partitioning are two parts:

Isolate applications that gain no benefit from cache but use up many cache slots just the same.

Prevent lower tier applications from “stealing” slots from higher tier applications.

In both cases isolating them forces the application to re-use the slots within its partition instead of taking the slots from another application. Solutions Enabler V7.4 and higher, user is able to use command symqos to manage DCP. In DCP configuration, there are five key settings that can be configured for each cache partition.

TargetPercent - Specifies the target cache percentage for a cache partition.

MinimumPercent - Specifies the minimum cache percentage for a cache partition.

MaximumPercent - Specifies the maximum cache percentage for a cache partition.

WritePendingLimit - Specifies the write pending limit percentage for a cache partition. Possible values are 40 - 80.

DonationTime - Specifies the donation time in seconds; the time for when idle cache is made available to other cache partitions.

Following are the command example:

Enabling and disabling cache partitions:

symqos -cp -sid SymmID enable | disable

Creating cache partitions:

symqos -cp -name PartitionName -sid SymmID create -target TargetPercent -min MinimumPercent -max MaximumPercent -wp WritePendingLimit -time DonationTime

For example, to create a cache partition named TestPartition on Symmetrix 123, enter:

symqos -cp -name TestPartition -sid 1234 -target 10 -min 5 -max 40 -wp 50 -time 10 create

To add devices to a partition, use the following commands:

symqos -cp -name PartitionName -sid SymmID add dev SymDevName

For example , to add device 001 to partition TestP on Symmetrix 123, use command:

symqos -cp -name TestP -sid 123 add dev 001

With Enginuity 5876 and higher, device pools can be added to and removed from cache partitions. To add a thin pool named Finance to the cache partition TestA, use command:

symqos -cp TestA -sid 123 addall -pool Finance –thin

For more DCP configuration through Solutions Eanbler command symqos, please refer the Symmetrix-Array-Controls-CLI-Product-Guide on EMC online support.

Author: Fenglin Li

             

iEMC APJ

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