Thin-provisioning is an implicit feature of all SSD devices and FCM is no exception. So it is possible to set 'none' in the additional capacity savings and fully provision the logical capacity at the software layer, and still rely only on the thin provisioning being performed in the hardware.
Hardware thin-provisioning will give the best maximum throughput for IO, so it can help satisfy the most demanding performance requirements. But software thin provisioning can still achieve high throughput rates.
The hardware thin-provisioning is finite - it comes from within the 3:1 savings that recent generations of FCM provide. Some environments want to provision empty capacity very generously to the host servers and then get flexibility to reassign actual capacity to where it is needed by unmapping old data and writing to different volumes. If these exceed 3:1 logical:compressed-physical then they still need to use software thin-provisioning. But these over-provisioned environments need careful management to not run out-of-space.
Many customers find hardware thin provisioning, i.e. additional capacity savings is none, the simplest to manage and provides them enough thin provisioning without excessive over-provisioning.
Software thin-provisioning will still be used for snapshots and change volumes because these are examples of use cases which need much more over-provisioning.
Thanks,
Carlos Fuente
Distinguished Engineer, IBM Storage Virtualize, FlashSystem & SVC Family
phone: +44-7795-917197
Unless otherwise stated above:
IBM United Kingdom Limited
Registered in England and Wales with number 741598
Registered office: Building C, IBM Hursley Office, Hursley Park Road, Winchester, Hampshire SO21 2JN
Original Message:
Sent: 10/30/2025 12:57:00 PM
From: William Thousand
Subject: Thin-Provisioning with FCM4 and standard pool
It appears that in a standard pool with all FCM modules with onboard compression, the thin-provisioning is happening kind of automatically by the modules regardless of the None/Thin-Provision setting on the volume. I'm assuming it's because with the compression it can't anticipate or actually reserve the space.
I added a new 5TB volume to a new standard pool with 21TB Physical / 99TB Logical and it says it's using 100MB Physical / 5TB logical.
So with this in mind, is there any advantage to using thin-provisioned volumes or should I just use fully allocated and keep an eye on the physical capacity?
------------------------------
William Thousand
------------------------------