HP 3PAR StoreServ Concepts Guide: HP 3PAR OS 3.1.3

TPVV Warnings and Limits
The TPVV volume size limit is 16 TB. When you create a TPVV, you can set an allocation warning
threshold and an allocation limit threshold.
• Allocation warning threshold: For volumes capable of allocating space on demand, the
user-defined threshold at which the system generates an alert. This threshold is a percentage
of the volume's virtual size, the size that the volume presents to the host.
• Allocation limit threshold: For volumes capable of allocating space on demand, the user-defined
threshold at which writes fail, preventing the volume from consuming additional resources.
This threshold is a percentage of the volume's virtual size, the size that the volume presents
to the host.
When you set TPVV allocation warnings and allocation limits, you must take into account the space
to be consumed by both the volume’s user data and the snapshot data.
The total amount of snapshot space consumed by a TPVV and its snapshots includes the data written
to the base volume and the data written to the snapshots. The size of the data written to the snapshots
equals the total writes to the base volume since the oldest existing read-only snapshot was created.
When deciding on the allocation warning and allocation limit thresholds for a TPVV, you can use
an estimate of the maximum write rate to compute the snapshot data growth rate.
• If there are no read-only snapshots, and the volume is not a physical copy or used for remote
copy, use the maximum write rate as the growth rate.
• If there are read-only snapshots, or if the volume is not a physical copy or used for remote
copy, use twice the maximum write rate as the growth rate.
• Set the allocation warning and limit thresholds based on the growth rate and the advance
warning you require before the volume reaches its limit, and writes fail.
Use the following formula to generate the allocation warning threshold:
where the value of n is as follows:
• For a TPVV without read-only snapshots, and that TPVV is not a physical copy or used for
remote copy, n=1.
• For a TPVV with read-only snapshots, or that TPVV is a physical copy or used for remote copy,
n=2.
For example, if a 1 TB TPVV with read-only snapshots has a maximum write rate of 1 GB per day
and you want 30 days warning prior to that TPVV reaching the allocation limit, use the following
calculation for the allocation warning percentage:
Virtual Volume Online Conversion
You can convert existing FPVVs to TPVVs and you can convert TPVVs to FPVVs on the array without
disrupting normal storage system operations and without requiring changes to any host applications
that access the virtual volumes. If a TPVV is using most of its allocated storage capacity, you might
choose to convert the volume to a fully provisioned volume to increase its storage capacity and
46 Virtual Volumes