Thin Volume overprovisioning

[miknotna]

Hi everyone!

We have 3PAR 8200 (OS 3.5).

On the configured SSD CPG we see, that Total used space is ~4 Tb and Estimated free usable is ~4.2 Tb. This CPG contains one thin volume (6 Tb provisioned).

This volume shows:

total used ~3.9 Tb

total reserved ~4 Tb

I don't clearly understand what "total reserved" means. Should we worry, that after volume reachs this "total reserved" limit, all IOs will stop?

 Volume is thin, 6 Tb provisioned and CPG has 4 Tb free, so I assume that we can reach 6 Tb on this volume. But I'm not sure. Thanks in advance!

[Satish04 · Accepted solution]

Hi miknotna,

In HPE 3PAR, the "total reserved" value refers to the space that has been allocated by the CPG to a Thin provisioned volume but has not been written to yet.
As data is written to the volume, the system has reserved space in order to ensure that the volume can continue to grow as long as the amount reserved remains the same.

It is estimated that your CPG has around 4.2 TB of free usable space, so it is possible to expand the Thin provisioned volume further. However, you should keep an eye on this space. In the event that CPG runs out of space, the volume will be unable to allocate additional space, which may cause IO errors or shut down the volume.

If your volume is Thin provisioned and the CPG has 4 TB free, theoretically, you can reach the volume's 6 TB limit.
However, if the CPG free space drops significantly, you might encounter problems as it tries to allocate more space.

To help you understand the terms, we have listed them below:

Total Used: The amount of data written to the volume.
Total Reserved: The space allocated for the volume of the CPG, but may not be fully utilized.
CPG Free Space: Estimates how much free space remain in the CPG.

Hope this helps.!

Regards,
Satish

[miknotna]

Hi Satish,

Thank you very much for information! We can stop worrying now )

[Satish04]

Hi miknotna,

We are glad to hear that your issue has been addressed. 

Regards,

Satish