Pool Shortfall (%) Total Data Reduction Savings (%) The percentage of space that is over-committed to the pools with thin-provisioned volumes.  For example, you commit 100 GiB of space to a thin-provisioned volume in a pool with a  capacity of 50 GiB. As the space is allocated to the thin-provisioned volume in increments of  10 GiB, the space available for allocation decreases and the shortfall in capacity becomes  more acute. To calculate the shortfall, the following formula is used: [(unallocatable space ÷ committed but unallocated space) × 100]  A pool shortfall occurs when you commit more space to the volumes in the pools than is  physically available to the pools. If the physical space available to the pools is less than the  committed virtual space, then the pools do not have enough space to fulfill the commitment to  the virtual space. For example, the physical capacity of the pools is 70 GiB, but 150 GiB of virtual space was  committed to the thin-provisioned volumes. If the volumes are using 50 GiB, then 100 GiB is  still committed to those volumes (150 GiB GLYPH<129> 50 GiB) with only 20  GiB of available pool space  (70 GiB GLYPH<129> 50 GiB). Because only 20 GiB of the pool space is available, 80 GiB of the  committed space cannot be allocated (100 GiB - 20 GiB). In this case, the percentage of  committed space that is unavailable is 80% [(80 GiB ÷ 100 GiB) × 100]. The advantage of using shortfall rather than a simple overprovisioning factor, is that shortfall  always has values between 0 and 100% and therefore is well suited for simple alerting that  can be applied to multiple pools.  Figure 8-20 explains the shortfall. The estimated amount and percentage of capacity that is saved by using data deduplication,  data compression, and thin provisioning. Figure 8-20 Shortfall 294  IBM FlashSystem 9200 and 9100 Best Practices and Performance Guidelines