To specify load balancing settings for an array

1. To launch the Array Settings wizard, open the DMP DSMs folder in the tree view.
2. Right-click the array that you are interested in and the array context menu appears.
3. Select Array Settings from the context menu.
4. The Array Settings welcome screen appears. Click Next to continue.
5. The Select Array Settings parameters screen appears.

   Select the load balancing option by clicking the appropriate radio button.

   SCSI-3 reservation support is required for all load balancing settings, except for Fail Over Only (Active/Passive). Refer to your array documentation to determine if your array supports SCSI-3 reservations before selecting any of these load balancing settings.

   • Round robin (Active/Active)

     This option ensures that load balancing is used for data transfers to and from an array. With this setting, DMP DSMs configures all paths in the array as active and I/O transfers occur on the paths each in turn, in a round-robin fashion.

   • Dynamic Least Queue Depth

     This option ensures that load balancing is used for data transfers to and from an array. With this setting, DMP DSMs configures all paths to the array as active and selects the path with the least number of I/O requests in its queue for a data transfer.

   • Balanced Path

     This policy is designed to optimize the use of caching in disk drives and RAID controllers. The size of the cache depends on the characteristics of the particular hardware. Generally, disks and LUNs are logically divided into a number of regions or partitions. I/O to and from a given region is sent on only one of the active paths. Adjusting the region size to be compatible with the size of the cache is beneficial so that all the contiguous blocks of I/O to that region use the same active path. The value of the partition size can be changed by adjusting the value of the tunable parameter, Block Shift.

     More details about this option are available.

     See Active/Active and Active/Passive settings.

   • Weighted Paths

     This option ensures that load balancing is used for data transfers to and from an array. With this setting, DMP DSMs configures all paths to the array as active and selects the path with the lowest weight for data transfer. The user assigns weights to designate which path is favored. If two or more paths have the same weight and are the lowest weight of all paths, then these paths are used each in turn, in round-robin fashion, for the data transfer.

     Note:

     This setting is available for A/PC and ALUA arrays only at the device level. It is not available at the array level.

   • Round robin with Subset

     This option ensures that load balancing is used for data transfers to and from an array. With this setting, DMP DSMs configures all paths to the array as active and uses a subset of paths. These paths are used each in turn, in round-robin fashion, for data transfer. The user specifies the subset of paths. The remaining paths are in standby mode.

     Note:

     This setting is available for A/PC and ALUA arrays only at the device level. It is not available at the array level.

   • Least Blocks

     This option ensures that load balancing is used for data transfers to and from an array. With this setting, DMP DSMs configures all paths to the array as active and selects the path with the least number of blocks of I/O in its queue for data transfer.

   • Fail Over Only (Active/Passive)

     This option has one primary path with the remaining path or paths on standby (backups) in case the primary path fails. The primary path is the only path that is used to transfer data. This option does not provide load balancing among paths. DMP DSMs sets a path to be the primary path. However, you may choose a specific path to be the primary path.

     See Specifying the primary path for an array or disk.

   There are specific DMP DSMs that work with specific families of hardware arrays. If your environment has more than one family of hardware arrays under control of DMP DSMs, then each family of hardware arrays works with specific DMP DSMs.

   If you want the selected load balancing setting to be the setting for all the arrays that this specific DMP DSMs driver controls, check the check box for All arrays under the DSM.

   The default load balancing setting of an array is dependent on the particular array. Consult the documentation for your storage array to determine the default setting and any additional settings it supports.

   In the sample screen that is shown below, the round robin (Active/Active) setting is selected.

   Click Next to continue.

6. The Array Settings summary screen appears displaying the settings for the array. Review the settings and click Finish to apply the settings and exit the wizard.

   For some load balance policies, such as round robin with Subset, additional specifications are required. The Array Settings wizard displays a screen before the summary screen to collect these specifications. Click Next after setting these specifications to continue to the summary screen.