How to provision compressed arrays

Hello friends! I hope all is well. This week I want to take a brief hiatus from performance and software to bring up a topic that is becoming increasingly important as people move towards the Storwize Gen3 and Flashsystem 9100 hardware. These hardware platforms premiered support for the IBM FlashCore Modules (FCM). Just like with the FS900 AE3 , these flash modules do hardware compression at the drive level. This makes them economical and exciting because you get a lot of extra flash space for your money. However, it is vitally important you think before you provision. Lets start by taking a look at how capacity looks in the dashboard in the GUI: Here we see the system has 21.42TB of physical capacity. However, if we go to create a volume we can create up to 99TB: This is where things get dangerous. If we check the lsarray output for the RAID set we see: IBM_FlashSystem:fab3:superuser>lsarray 0 | grep capacity capacity 99.1TB physical_capacity 21.42TB physical_free_ca