Pool subscription limit

The value of using a subscription limit is to manage the maximum amount of over-provisioning that is acceptable for a pool. By managing the pool subscription limit, you can control the potential demand for storing data that might exceed the pool capacity.

Note

If you are using the pool comprised of pool-VOLs assigned by accelerated compression-enabled parity groups, the pool subscription limit is defined with respect to the pool capacity not reserved for writing. In this case, the free area of the pool must be monitored even if the subscription limit is defined to 100%.

If you do not want to monitor the free area of the pool, specify the subscription limit conforming to the following formula: 

Pool capacity / Pool capacity reserved for data writing × Subscription limit = 100%

For example, if 100 TB of the pool capacity and 80 TB of the pool capacity reserved for writing exist, specify 80% as the subscription limit.

The subscription limit is the ratio (%) of the total DP-VOL capacity that has been configured to the total capacity of the pool. When the subscription limit is set, you cannot configure another DP-VOL if the new DP-VOL capacity would cause the subscription limit to be exceeded.

The subscription limit includes pages required to store user data and control information. The total capacity of DP-VOLs that are created from the pool is smaller than the subscription limit capacity. The formula used to calculate the required pages for one DP-VOL includes the control information. To determine the total pages required in a pool, multiply the number of calculated pages by the number of DP-VOLs. The value enclosed in ceil( ) must be rounded up to the nearest whole number. The number of pages for the DP-VOL including the control information equals: 

Number of pages for the 
    DP-VOL including the control information = ceil((One 
		  DP-VOL capacity (MB) + ceil(One 
		  DP-VOL capacity (MB) / 3,145,548 (MB)) * 4 (Pages) * 42 (MB)) / 42 (MB))

For example, if the pool capacity is 100 GB and the subscription limit is 150%, you can configure up to a total of 150 GB of capacity to the DP-VOLs related to the pool.

The following figure depicts setting the subscription limit of pool capacity.

Parent Topic
  • Thresholds for monitoring pools

    Dynamic Provisioning monitors pool capacity using thresholds. A threshold is the proportion (%) of the used capacity of the pool to the total capacity of the pool, or the proportion (%) of the physical used capacity of the pool to the total capacity reserved for writing of the pool.

Child Topics