Cache partitions

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View cache utilization statistics for a TS7700 Tape Attach, Cloud, and Object store where the cache is made up of multiple partitions.

The cache utilization table displays information for each active partition in the cache. Each displayed partition can be expanded to show any preference or retention group defined within the partition.
Table 1. Cache utilization table information
Column name Description
Partition Number Possible values are 0-7. "Inserted" logical volumes are those with a -1 partition, meaning that there is no consistent data yet.

You cannot modify the values in this column. The primary partition is identified by an icon next to the partition number, you can have one primary Logical Volume and one Primary Object Partition.

The blue star has always represented the primary partition for tape/cloud partitions.

If DS8K offload is implemented and we have object partitions, the green star represents the "primary object partition".
Name The name of the active partition. You can expand the partition entry to display any preference and retention group assignments. Group information is displayed only if that group has a Used value greater than 0.
Resident-only retention groups
Prefer Keep
Removal candidates in this group are removed after removal candidates in the Prefer Remove group are removed.
Prefer Remove
Removal candidates in this group are removed prior to removal candidates in the Prefer Keep group.
Pinned
Copies of volumes in this group are never removed from the accessing cluster. The volume copy retention time does not apply to volumes in this group. Volumes in this group that are subsequently moved to scratch become priority candidates for removal.
CAUTION:
Care must be taken when assigning volumes to this group to avoid cache overruns.
FlashCopy
Volumes in this group are flash copies.
Partition preference groups
PG0
Volumes in this group have preference to be removed from cache over other volumes.
PG1
Volumes in this group have preference to be retained in cache over other volumes. A "least recently used" algorithm is used to select volumes for removal from cache if there are no volumes to remove in preference group 0.

Within both groups, each partition has one of the following states:

Premigrated
Volumes were read from cache and written to a physical volume.
In premigration queue
Volumes are slated to be read from cache and written to a physical volume.
Waiting for delay premigration
Volumes are slated to be read from cache and written to a physical volume, but those operations are temporarily delayed.
Type The type of data stored in the partition. Possible values are virtual tape and object.
Used The amount of used data in the partition. The total amount of used data that is shown for all groups in a partition approximately equals the total amount of used data in the partition as a whole. By default, data is shown in decimal values in increments of TB, where the minimum size of 0.01 TB indicates from 1 GB to 14.44 GB. You can use the Actions menu to change the display to show binary values (TiB).
Capacity The amount of used space shown visually as a percentage of the total allocated capacity. The maximum size of the partition or allocated cache is displayed to the right of the capacity bar image. You can hover over the bar to display the numeric value of the used cache. If flash copies exist, the amount is displayed in orange. You can hover over it to display the numeric value and its percentage.
Note: If a partition is in an over-committed state, a warning icon is displayed on the left edge of the capacity bar image.
By default, data is shown in decimal values in increments of TB, where the minimum size of 0.01 TB indicates from 1 GB to 14.44 GB. You can use the Actions menu to change the display to show binary values (TiB).
Volumes The number of volumes in cache for the partition. Migrated volumes are not included in this count.
% of Cache The percentage of total cache allocated to a partition.
Premigration Size The amount of data that is queued for premigration. This column displays data for partitions only. The total number of volumes that are shown for all groups in a partition equals the total number of volumes in the partition as a whole.
Note: This column is hidden by default. Click the customize column display icon to the right of the table heading row to add this column to the table.
By default, data is shown in decimal values in increments of TB, where the minimum size of 0.01 TB indicates from 1 GB to 14.44 GB. You can use the Actions menu to change the display to show binary values (TiB).
Cache to Copy The amount of data to be copied to other clusters. This column is not displayed if the cluster is a stand-alone machine. The total amount of data that is shown for all groups in a partition equals the total amount of data in the partition as a whole.
Note: This column is hidden by default. Click the customize column display icon to the right of the table heading row to add this column to the table.
By default, data is shown in decimal values in increments of TB, where the minimum size of 0.01 TB indicates from 1 GB to 14.44 GB. You can use the Actions menu to change the display to show binary values (TiB).
Delayed Premigration Limit The maximum amount of data that can exist in a delayed premigration state. This column displays only data for partitions. This value is an upper limit that you select when creating partition. The total amount of used data in all Delayed Premigration preference groups in any partition.
Note: This column is hidden by default. Click the customize column display icon to the right of the table heading row to add this column to the table.
By default, data is shown in decimal values in increments of TB, where the minimum size of 0.01 TB indicates from 1 GB to 14.44 GB. You can use the Actions menu to change the display to show binary values (TiB).
Note: An object partition will always be 0 and can not be adjusted.
Objects The number of Objects stored in the object data partition.
You can add, modify, or delete a partition, or change the appearance of information shown on the cache utilization table.
To... Do this:
Create a partition
  1. Click Create Partition.
    Note: Additional object cache partitions cannot be added. Only logical volume cache partitions for tape or cloud can be created
  2. Enter a unique partition name. This value must be one to 20 characters long and must be composed of alphanumeric characters. Blank spaces are also allowed, along with the following characters:
    • #
    • @
    • $
  3. Enter a value for Allocated size. This value must be an increment of 1 TB. The minimum value is 1 TB.
  4. Enter a value for the Delayed Premigration Limit (Not applicable to Object partitions). This value must be an increment of 500 GB. The minimum value is 500 GB, and the maximum value cannot exceed the total allocation size of the partition minus 500 GB.
  5. To make the new partition the primary partition, check the Primary partition check box.
  6. Click Create.
Restrictions:
  1. You can use this option to create new partitions only. You cannot use this option to create a resident-only partition.
  2. You cannot create more than 7 partitions.
  3. You cannot create a partition if the available free space in the resident-only partition (CP0) is less than or equal to 2 TB.
  4. You cannot create a new partition if any existing partition is in the overcommitted state, as reported in the Configured Capacity column.
  5. You cannot create a new partition if a FlashCopy for DR test is in progress.
Resize a partition You can change the allocation size and the delayed premigration limit for a partition.
  1. Select the partition that you want to change.
  2. Click Actions > Resize.
  3. Change values for the allocation size, delayed premigration limit, or both.
  4. Click Resize.
Restrictions:
  1. If you decrease the allocated size to a value that is lower than the current used amount, the partition enters the overcommitted state and a warning is displayed. You can continue to resize a partition in the overcommitted state, but performance can be affected.
  2. You cannot increase the allocated size to a value that exceeds the maximum free space value.
  3. You cannot resize a partition if a FlashCopy for DR test is in progress.
  4. By default, data is resized in TB increments, where the minimum size of 1 TB.
  5. Delayed Premigration Limit is not utilized for object partitions. Only logical volume partitions can have the Delayed Premigration Limit resized.
Rename a partition
  1. Select the partition that you want to change.
  2. Click Actions > Rename.
  3. Enter a unique partition name. This value must be one to 20 characters long and must be composed of alphanumeric characters. Blank spaces are also allowed, along with the following characters:
    • #
    • @
    • $
  4. Click Rename.
Change the primary partition
  1. Select the partition that you want to designate as the new primary partition.
  2. Click Actions > Designate Primary Partition.
  3. Click Yes.
Restrictions:
  1. Properties of the new primary partition become effective for all volumes that are not assigned to a partition, including those volumes that were assigned to a partition that no longer exists.
  2. You cannot change a primary partition if a FlashCopy for DR test is in progress.
  3. You cannot change the primary partition for an object partition.
Delete a partition
  1. Select the partition that you want to delete.
  2. Click Actions > Delete.
  3. Specify the type of partition:
    1. If the selected partition is not the primary partition, click Yes.
    2. If the selected partition is the primary partition and only one other partition exists, click Yes.
    3. If the selected partition is the primary partition and multiple extra partitions exist, select a new primary partition from the Select a new primary partition drop-down menu. Then, click Make Primary.
  4. You can not delete the last remaining Object partition.
Restrictions:
  1. A partition must be empty before it can be deleted. Partitions that contain active volumes cannot be deleted.
  2. You cannot delete a partition if a FlashCopy for DR test is in progress.
  3. If the deletion request fails with the message Deletion of partition [id] is failed because there are active volumes associated with the partition, it means that migrated virtual volumes are associated with the partition. This can occur even when the partition itself does not contain any virtual volumes. You can locate the virtual volumes by completing a virtual volume search and searching on the partition number.You cannot delete a partition if there are migrated virtual volumes associated with the partition.
Change measurement units shown You can show cache utilization measurements on the table in binary or decimal units. Click Actions > Show in binary units or Actions > Show in decimal units to change units of cache measurement. The following table fields change in response:
  • All values in the Used column
  • Configured Capacity values
  • Premigration Size values
  • Cache to Copy values
  • Delayed Premigration Limit values
View statistics for a partition
  1. Select the partition that you want to view cache statistical data for.
  2. Click Actions > View Statistics.
  3. Select a description of statistical data from the drop-down menu. Data that is displayed depends on partition type.
    Partitions
    Statistics available for partitions include:
    Mean duration that virtual volumes have remained in cache
    The longest time a virtual volume has remained in cache preceding the end of the defined time period (last 4 hours, 48 hours, 35 days). The longest time a virtual volume has remained in cache is sampled every hour and all samples for the defined period are averaged together. Each hourly sample discards "outliers" that are greater than one and a half times the interquartile range past the third quartile. The outliers are small numbers of virtual volumes that are not representative of the cache as a whole.
    Mean duration is displayed for any of the following groups if they contain active volumes:
    • PG0
    • PG1
    • Delayed Premigration
    Number of virtual volumes migrated
    Rolling average number of virtual volumes that are migrated to a cache preference group. This statistic is only visible if the cluster possesses a physical library.
    Number of migrated volumes is displayed for the following groups:
    • PG0
    • PG1
    Resident-only partitions
    Statistics available for resident-only partitions include:
    Mean duration that virtual volumes have remained in cache
    Refer to previous definition in Partitions section.
    Mean duration is displayed for any of the following groups if they contain active volumes:
    • Prefer Keep
    • Prefer Remove
    • Pinned
    • FlashCopy
    Virtual volumes removed from cache
    The number of virtual volumes that are removed from cache within the last 4 hours, according to retention group.
    The number of virtual volumes that are removed is displayed for the following groups:
    • Prefer Keep
    • Prefer Remove
View properties of a partition
  1. Select the partition that you want to view a summary of properties for.
  2. Click Actions > Properties.
Partitions
Properties available for partitions include:
  • Partition name and number
  • Type
  • Volumes
  • Configured Capacity
  • Used size
  • % of total cache (the remaining properties are cloud and tape attach only)
  • Delay Premigration size
  • Delayed Premigration Limit
  • Cache to Copy
  • Preference Group 0 premigrated
  • Preference Group 1 premigrated
  • Preference Group 0 in premigration queue
  • Preference Group 1 in premigration queue
  • Preference Group 0 waiting for delay premigration
  • Preference Group 1 waiting for delay premigration
  • Number of virtual volumes migrated (which are not available or displayed for Cloud-Enabled Clusters).
Resident-only Partitions:
Properties available for resident-only partitions include:
  • Partition name and number
  • Type
  • Volumes
  • Configured Capacity
  • Used size
  • % of total cache
  • FlashCopy size
  • Cache Removal Threshold
  • Cache to Copy
  • Prefer keep size
  • Prefer remove size
  • Pinned size
Object Partitions:
Properties available for Object partitions include:
  • Partition name and number
  • Type
  • Objects
  • Configured Capacity
  • Used size
  • % of total cache
For data descriptions, see Table 1.