System option modes for ShadowImage

To provide greater flexibility, the storage systems have additional operational parameters called system option modes (SOMs) that allow you to tailor the storage system to your unique operating requirements. The SOMs are set on the service processor (SVP) by your service representative. Review the SOMs for your storage system, and work with your service representative to ensure that the appropriate SOMs for your operational environment are configured on your storage system.

The following table lists and describes the SOMs that apply to ShadowImage and ShadowImage for Mainframe. For a complete list of SOMs, see the System Administrator Guide for your storage system.

NoteThe SOM information might have changed since this document was published. Contact customer support for the latest SOM information.

Table 1: System option modes for ShadowImage

Mode

Category

Description

Default

MCU/RCU

80

ShadowImage

In response to the Restore instruction from the host, if neither Quick nor Normal is specified, the following operation is performed.

Mode 80 = ON: Normal Restore / Reverse Copy is performed.

Mode 80 = OFF (default): Quick Restore is performed.

Notes:

  1. This mode is applied when the specification for Restore of SI is switched between Quick (default) and Normal.
  2. The performance of Restore differs depending on the Normal or Quick specification.

OFF

-

87

ShadowImage

Determines whether NormalCopy or QuickResync, if not specified, is performed at the execution of pairresync by CCI.

Mode 87 = ON: QuickResync is performed.

Mode 87 = OFF (default): NormalCopy is performed.

OFF

-

122

ShadowImage

For Split or Resync request from the Mainframe host and Storage Navigator.

Mode 122 = ON: By specifying Split or Resync, Steady/Quick Split or Normal/Quick Resync is respectively executed in accordance with Normal/Quick setting.

Mode 122 = OFF (default): By specifying Split or Resync, Steady/Quick Split or Normal/Quick Resync is respectively executed in accordance with Normal/Quick setting.

For details about pairsplit/pairresync command behavior, contact customer support (see SOM122 sheet).

Notes:

  1. Executing the pairresync command from CCI may be related to the SOM 87 setting.
  2. When performing At-Time Split from CCI, set this mode to OFF, or specify the environment variable HORCC_SPLT for Quick. Otherwise, Pairsplit may turn timeout.
  3. This mode becomes effective after specifying Split/Resync following the mode setting. The mode function does not work if it is set during the Split/Resync operation.

OFF

-

459

ShadowImage

When the S-VOL of an SI/SIz pair is an external volume, the transaction to change the status from SP-PEND to SPLIT is as follows:

Mode 459 = ON: When suspending an SI pair: The copy data is created in cache memory. When the write processing on the external storage completes and the data is fixed, the pair status will change to SPLIT.

Mode 459 = OFF (default): When suspending an SI pair: Once the copy data has been created in cache memory, the pair status will change to SPLIT. The external storage data is not fixed (current spec).

OFF

-

467

ShadowImage

Snapshot

Volume Migration

Universal Volume Manager

For the following features, the current copy processing slows down when the percentage of “dirty” data is 60% or higher, and it stops when the percentage is 75% or higher. Mode 467 is provided to prevent the percentage from exceeding 60%, so that the host performance is not affected.

  • SI
  • Snapshot
  • UVM
  • Volume Migration

Mode 467 = ON (default): Copy overload prevention. Copy processing stops when the percentage of “dirty” data reaches 60% or higher. When the percentage falls below 60%, copy processing restarts.

Mode 467 = OFF: Normal operation. The copy processing slows down if the dirty percentage is 60% or larger, and it stops if the dirty percentage is 75% or larger.

Caution: This mode must always be set to ON when using an external volume as the secondary volume of any of the applicable replication products.

Notes:

  1. It takes longer to finish the copy processing because it stops for prioritizing the host I/O performance.
  2. This mode supports background copy only. The processing to copy the pre-update data to the S-VOL, which occurs when overwriting data to uncopied slots of P-VOL in Split processing or reading or writing data to uncopied slots of S-VOL, is not supported.
  3. Check the write pending rate of each CLPR per MP blade. Even though there is some free cache capacity in the entire system, if the write pending rate of an MP blade to which pairs* belong exceeds the threshold, the copy operation is stopped.

    *Applies to pairs of SI, SIz, FCv2, FCSE, Snapshot, and Volume Migration.

ON

-

704

ShadowImage

Volume Migration

To reduce the chance of MIH, this mode can reduce the priority of ShadowImage, Volume Migration, or Resync copy internal IO requests so that host IO has a higher priority. This mode creates new work queues where these jobs can be assigned with a lower priority.

Mode 704 = ON: Copy processing requested is registered into a newly created queue so that the processing is scheduled with lower priority than host I/O.

Mode 704 = OFF (default): Copy processing requested is not registered into a newly created queue. Only the existing queue is used.

Notes:

  1. Apply this mode when the load of host I/O to an ECC that uses ShadowImage or Volume Migration is high and the host I/O processing is delayed.
  2. If the PDEV is highly loaded, the priority of Read/Write processing made by ShadowImage, Volume Migration, or Resync may become lower. As a consequence the copy speed may be slower.

OFF

-

733

ShadowImage

Volume Migration

This mode enables to suspend Volume Migration or Quick Restore operation during LDEV-related maintenance.

Mode 733 = ON: Volume Migration or Quick Restore operation during LDEV-related maintenance is not suspended.

Mode 733 = OFF (default): Volume Migration or Quick Restore operation during LDEV-related maintenance is suspended.

Notes:

  1. Note that behavior when the mode is set to ON and OFF is reversed between USP V/VM and VSP/HUS VM and later.
  2. This mode should be applied to perform Volume Migration or Quick Restore during maintenance operation.
  3. Set mode 733 to ON if you want to prioritize the Volume Migration or Quick Restore operation over maintenance activities. In this case, maintenance activities may fail when the Volume Migration or Quick Restore operation works during the maintenance activities.
  4. An LDEV-related maintenance operation such as LDEV installation/removal may fail when Volume Migration or Quick Restore takes place.

OFF

-

855

ShadowImage

Volume Migration

By switching the mode to ON/OFF when ShadowImage is used with SOM 467 set to ON, copy processing is continued or stopped as follows.

Mode 855 = ON: When the amount of dirty data is within the range from 58% to 63%, the next copy processing is continued after the dirty data created in the previous copy is cleared to prevent the amount of dirty data from increasing (copy after destaging). If the amount of dirty data exceeds 63%, the copy processing is stopped.

Mode 855 = OFF (default): The copy processing is stopped when the amount of dirty data is over 60%.

For details, contact customer support (see SOM855 sheet).

Notes:

  1. This mode is applied when all the following conditions are met
    • ShadowImage is used with SOM 467 set to ON.
    • Write pending rate of an MP blade that has LDEV ownership of the copy target is high
    • Usage rate of a parity group to which the copy target LDEV belongs is low.
    • ShadowImage copy progress is delayed.
  2. This mode is available only when SOM 467 is set to ON.
  3. If the workload of the copy target parity group is high, the copy processing may not be improved even if this mode is set to ON.

OFF

-

930

Dynamic Provisioning

Dynamic Tiering

ShadowImage

When the mode is set to ON, all of the zero data page reclamation operations in processing are stopped. (Also the zero data page reclamation cannot be started.)

* Zero data page reclamation by WriteSame and UNMAP functions, and IO synchronous page reclamation are not disabled.

Mode 930 = ON: All of the zero data page reclamation operations in processing are stopped at once. (Also the zero data reclamation cannot be newly started.)

Mode 930 = OFF (default): The zero data page reclamation is performed.

For details about interactions with SOM 755, contact customer support (see SOM930 sheet).

Notes:

  1. This mode is applied when stopping or disabling zero data page reclamation by user request is required.
  2. When the mode is set to ON, the zero data page reclamation does not work at all.

    * Zero data page reclamation by Write Same and UNMAP, and IO synchronous page reclamation can work.

  3. When downgrading micro-program to a version that does not support the mode while the mode is set to ON, set the mode to OFF after the downgrade.

    * Because the zero data page reclamation does not work at all while the mode is set to ON.

  4. The mode is related to SOM 755.

OFF

-

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