PowerFlex How To Calculate Spare Capacity

Steps

An even number of SDSs across all the SPs in the PD (Protection Domain)

The spare capacity percentage should be set to 1 out of 'n' SDSs in the SP, rounded up:

1 / <EVEN number of SDSs in the SP> * 100 = <SP spare capacity>

For example, in a PD with 6 SDSs per SP, the spare capacity percentage per SP will be rounded up to 17%:

1 / 6 * 100 = 16.66666666666667%

In case the SP has 10 or more SDSs, it is advised to have at least 10% set as spare capacity.

An uneven number of SDSs across all the SPs in the PD
The spare capacity percentage should be set to 1 out of the largest number of SDSs in a specific SP, rounded up:

1 / <UNEVEN number of SDSs in the SP> * 100 = <SP spare capacity>

For example, in a PD with 3 SPs, 2 SPs with 3 SDSs, and one SP with 5 SDSs, the spare capacity percentage per SP will be 20%:

1 / 5 * 100 = 20%

In case the SP has 10 or more SDSs, it is advised to have at least 10% set as spare capacity.

An uneven capacity of SDSs across all the SPs in the PD
The spare capacity percentage should be calculated for the SDS that has the largest capacity times the servers willing to be lost in a specific SP, rounded up:

<HIGHEST SDS capacity> * 100 / <TOTAL SP capacity> * <Servers willing to LOSE> = <SP spare capacity>

For example, if an SDS has the highest capacity of 2 TB in an SP that has a total capacity of 10 TB, then the SDS's capacity is 20% of that total, with two servers that are to be lost:

2 * 100 / 10 * 2 = 40%

Set spare capacity

Set the spare capacity percentage by running the following command on the Primary MDM:

# scli --modify_spare_policy --protection_domain_name <protection domain name> --storage_pool_name <storage pool name> --spare_percentage <percentage>

For example:

# scli --modify_spare_policy --protection_domain_name PD1 --storage_pool_name SP1 --spare_percentage 15