PowerMax 2000, 8000, VMAX All-Flash: Effective Used Capacity, SRP Utilization when Migrating

Utilization of the Storage Resource Pool (SRP) must be measured.

Unisphere may issue an alert regarding SRP utilization.

Monitoring a storage array's utilization is important. Historically, this has been a relatively simple calculation; some available GB compare with how many of them have been used.

In HYPERMAX OS (5977 and later), compression was introduced for VMAX All-Flash arrays. This complicates the previously simple calculations because each track can potentially store more data. Thus, the number of available GB within the SRP is no longer predetermined, creating a "moving target" for the maximum capacity value as the SRP is gradually filled with data. With PowerMax 2000 and 8000 arrays and PowerMaxOS, deduplication was introduced and this further reduces SRP utilization, as this must also be considered.

Multiple capacity values can be found for the SRP when using Unisphere for PowerMax or performing the 'symcfg show -srp -detail' command:

• Effective Used Capacity (%): This represents the best measure of utilization the microcode can produce, and is based on existing data reduction statistics. It considers all data reduction components (deduplication, current compression, potential compressibility, Activity-Based Compression, and so forth) to provide the current utilization compare with the projected maximum SRP capacity. This is unique to each SRP based on data reduction and activity-based use of the data stored within it.
• Usable Capacity (GB): The physical capacity of the SRP (not the maximum amount of data that can be stored in the SRP).
• Used Capacity (GB): This is the used physical capacity of the SRP. This is a purely physical value, and does not account for trends in data reduction. This is not a reliable measure of the amount of data that is being stored within this used space.
• Free Capacity (GB):  This is the free physical capacity of the SRP. This is a purely physical value, and does not account for trends in data reduction. This is not a reliable measure of the amount of data that can potentially be stored within the remaining free space.
• Subscribed Capacity (GB): This is the current measure of the amount of storage has been provisioned to hosts from this SRP. This value has no direct correlation to the utilization of the SRP.

Notes Regarding Migrations:

• Incoming migrations constitute data of unknown reducibility to the target SRP. Most of this data is not reduced during the migration, initially being stored uncompressed (at a 1:1 ratio) due to the rapid influx of new data. 
• Background processes including snapshots, VMotion, ODX stalls and potentially fails if the SRP reaches 90% Effective Used.

Effective Used Capacity is the best measure of SRP utilization.

As of PowerMaxOS 5978 and Solutions Enabler, Unisphere 9.x, SRP alerts are based on Effective Used Capacity, rather than the previous Used Capacity.

• If required, an SRP alert can be set to notify you when the SRP capacity needs attention.
• Default notifications regarding SRP Full are sent at 80%, 87%, 90%, 95%, and 99%.

If you believe for any reason that the SRP alarm is generated incorrectly, contact the Dell Technologies Support or your local Dell Technologies Service representative and include this article number.

Best Practices to prevent host or application impact during migrations:

• Migrations should plan to remain below 90% Effective Used at a 1:1 ratio (without expectation of data reduction).
• The migrated data is evaluated over the first several days as hosts access it in the new SRP.
• Once reduction has stabilized for the recently migrated data, additional migrations can be considered using the same 1:1 planning.