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About Virtual Partition Manager

Your storage system can connect to multiple hosts and can be shared by multiple users, which can result in conflicts among users. For example, if a host issues many I/O requests or reads or writes a large amount of data, the I/O performance of other hosts may be affected. Virtual Partition Manager allows you to create multiple virtual cache memories called cache logical partitions (CLPRs), each allocated to different hosts, to prevent contention for cache memory and improve I/O performance.

A cache logical partition is a pool of the cache and parity groups in the storage system. Partitioning cache into one or more CLPRs allows storage administrators to dedicate individual CLPRs to a different host, preventing I/O contention for cache memory. Partitioning cache dedicates cache resources for exclusive use by specific applications to maintain priority and quality of service for business-critical applications. Storage administrators can secure or restrict access to storage resources to ensure confidentiality for specific applications. By dedicating resources to each partition as needed, a high quality of service can be maintained for all users.

You can allocate one of the following for a CLPR:

  • A parity group
  • An external volume
  • A virtual volume of Dynamic Provisioning or Thin Image

Use case for cache logical partitioning

The following figure shows three branch offices and 128 GB of cache memory partitioned into one 40-GB segment for each office. The host for branch A has a heavy I/O load. Because the cache memory is partitioned, that heavy I/O load cannot affect the cache memory for branch B or branch C.

GUID-1DBCDFB0-D2A7-42C1-A389-FD1296DDF187-low.png

CLPR names

CLPR0 is the default CLPR in the storage system. If you have not yet created any cache logical partitions, all cache belongs to CLPR0.

The following table lists the reserved CLPR names and corresponding CLPR IDs. These CLPR names are reserved with each CLPR ID. You cannot use another CLPR ID. For example, if the CLPR ID is 1, you cannot change the CLPR name to CLPR2.

NoteYou can create a maximum of 32 CLPRs including CLPR0, which is created by default.

CLPR ID

CLPR name

CLPR ID

CLPR name

0

CLPR0

16

CLPR16

1

CLPR1

17

CLPR17

2

CLPR2

18

CLPR18

3

CLPR3

19

CLPR19

4

CLPR4

20

CLPR20

5

CLPR5

21

CLPR21

6

CLPR6

22

CLPR22

7

CLPR7

23

CLPR23

8

CLPR8

24

CLPR24

9

CLPR9

25

CLPR25

10

CLPR10

26

CLPR26

11

CLPR11

27

CLPR27

12

CLPR12

28

CLPR28

13

CLPR13

29

CLPR29

14

CLPR14

30

CLPR30

15

CLPR15

31

CLPR31

Requirements for using performance functions

The following lists and describes the system requirements and permissions for using the performance management functions.
  • License keys for performance management: The license keys for the following software products must be installed on the storage system:
    • Performance Monitor
    • Server Priority Manager
    • Virtual Partition Manager

    For details about installing license keys, see the System Administrator Guide.

  • Access privileges for Device Manager - Storage Navigator: Administrator access for Device Manager - Storage Navigator or write access for the performance management software products is required to perform operations. Users without Administrator access or write access can only view the performance management information and settings. You need specific administrator roles to use the following functions:
    • Performance Monitor: Storage Administrator (Performance Management)
    • Server Priority Manager, Virtual Partition Manager: Storage Administrator (System Resource Management)
  • Java: Java is required to use Server Priority Manager on the Device Manager - Storage Navigator computer. For details about installing Java and configuring Device Manager - Storage Navigator, see the System Administrator Guide.
  • Secondary windows on Device Manager - Storage Navigator:

    You must enable secondary windows if you plan to use any of the following functions in Device Manager - Storage Navigator (HDvM - SN):

    • Login Message function
    • Data Retention Utility
    • Server Priority Manager
    • Compatible PAV
    • Compatible XRC
    • Volume Retention Manager
    Java and some settings of Device Manager - Storage Navigator are required for the secondary windows. For details about enabling and using the secondary windows, see the System Administrator Guide.
  • Cache memory for Virtual Partition Manager: Use of Virtual Partition Manager might require additional cache memory in your storage system.

Cautions and restrictions for Virtual Partition Manager

  • Increased cache memory requirements

    Install additional cache memory before partitioning cache. Adding cache memory after CLPRs have been created is difficult and can be problematic. For details, see Calculating cache capacity.

  • Impact on host performance

    Creating and changing cache logical partitions can significantly degrade host performance and should only be performed during the initial installation and setup of the storage system or during maintenance. If you must perform these changes on a production machine, use Hitachi Performance Monitor to verify that the write pending rate and sidefile occupancy rate of the CLPR and CLPR0 satisfy the following formulas on all MP unit:

    • For CLPR with decreased cache capacity
      Write pending rate x cache capacity before operation / 
      cache capacity after operation < 30%
      Sidefile occupancy rate x cache capacity before operation / 
      cache capacity after operation < sleep wait threshold x 50%
    • For CLPR with increased cache capacity
      Sidefile occupancy rate < sleep wait threshold x 50%
  • When you move resources in CLPRs, make sure that the writing pending rates of the MP unit for each CLPR are less than 50 percent at both the source and the destination. The process for changing the CLPR settings will be suspended until the write pending rates of each MP unit become less than 50 percent.

    When you perform the following CLPR operations successively, you must wait for the current CLPR operation to complete before starting the next one. If the next CLPR operation is performed before the completion of the current CLPR operation, the last operation is enabled. Verify the CLPR settings, and then retry the operation:

    • Creating a CLPR
    • Deleting a CLPR
    • Moving resources within a CLPR
    • Editing CLPR settings

    As an exception, you can move resources in a CLPR while resources are being moved in another CLPR.

  • Duration of cache partition operations

    Adding or changing CLPR definitions or configurations can take hours to complete. After a CLPR operation has been started, you cannot cancel or modify the process until the operation is complete.

  • Interoperability restrictions for cache partitioning

    Application

    Behaviors

    ShadowImage/ ShadowImage for Mainframe

    You cannot use ShadowImage or ShadowImage for Mainframe Quick Restore functions that affect multiple CLPRs.

    Volume Migration

    You cannot use Volume Migration when it affects multiple CLPRs.

    Universal Replicator

    Universal Replicator data volumes and journal volumes can belong to different CLPRs. All journal volumes in the same journal must belong to the same CLPR. If not, an error occurs.

Cache partitioning workflow

  1. Calculate the cache capacity required for your needs, taking into account other features and functions that also have cache capacity requirements. For details, see Calculating cache capacity.
  2. If needed, install additional cache memory in your storage system.
  3. Determine an appropriate time to create CLPRs and migrate resources to the new CLPRs. Creating CLPRs and migrating resources can significantly degrade host performance and should be performed during the initial installation and setup of the storage system or during maintenance.
  4. Create the CLPRs and migrate resources to the new CLPRs. For details, see Creating a CLPR and Migrating resources to and from a CLPR.
  5. Manage the CLPRs as needed.

    After a CLPR has been created, you can change the CLPR name and CLPR cache capacity. For details, see Editing an existing CLPR.