Dell PowerFlex Appliance with PowerFlex 3.x Administration Guide

Calculate journal capacity to allocate

The journal is shared between all of the replicated RCGs in the protection domain.

1. Select the storage pool from which to allocate the journal capacity.
2. Consider the minimal requirements needed (28 GB multiplied by the number of SDR sessions). Journal capacity will be the maximum of these two factors.
   Consider the expected outage time. The minimal outage allowance is one hour, but at least three hours are recommended.
3. Calculate the journal capacity needed per application: maximal application throughput x maximum outage interval.
4. Calculate the percentage of capacity based on the previously calculated needs as journal capacity is defined as a percentage of storage pool capacity.

   For example, an application generates 1 GB/s of writes. The maximal supported outage is three hours (3 hours x 3600 seconds = 10800 seconds). The journal capacity needed for this application is 1 GB/s x 10800 s = ~10.547 TB. Since the journal capacity is expressed as a percentage of the storage pool capacity, divide the 10.547 TB by the size of the storage pool usable capacity, which is 200 TB:100 x 10.547 TB/200 TB = 5.27% round this up to 6%.

5. Repeat this for each application being replicated.
   NOTE:When the storage pool capacity is critical, capacity cannot be allocated for new volumes or for expanding existing volumes. This behavior must be considered when planning the capacity available for journal usage. The volume usage must leave enough capacity available in the storage pool to allow provisioning of journal volumes. The plan should account for the storage pool staying below critical capacity even when the journal capacity is almost fully utilized.