Over provisioning means, that in total more space is being assigned and promised to the  hosts. They can possibly try to store more data on the storage subsystem, as physical  capacity is available. This will result in an out-of-space condition.  Note:  It is extremely important to avoid this situation and to monitoring is very important! Its also important to keep free space for Garbage collection in the background , “DRP  internal details” on page 60 and Chapter 4, “Storage Pools” on page 55.  Data Reduction technologies will give back some space. If the space that’s used for the data  can be reduced, the saved up space can be used for other data. But keep in mind that,  depending on the type of data, deleting might not result in freeing up much space.  Just imagine if you have three identical/almost identical files on a file system which have been  deduplicated. This resulted in getting a quite good compression ratio (3 files - but stored only  once). If you now delete one file, you would not gain more space, because the deduplicated  data has to stay on the storage, because two other versions see the data. Similar results  might be seen when using several FlashCopies of one source. Table 8-3 shows alerts for IBM FlashSystem 9100 systems based on Array or Pool level.  Other alerts are possible as well, but generally % alerts are best suited, as the alert definition  applies to all pool in a storage system. In this part of the book we show how to deploy IBM Spectrum Control or IBM Storage Insights  Pro in order to monitor storage capacity and set up thresholds to notify and prevent us from  running out of space. The following example shows how to create an alert to get status Information about the  remaining physical space on an IBM FlashSystem 9100. Firstly, assign a severity to an alert. Assigning a severity can help you more quickly identify  and address the critical conditions that are detected on resources. The severity that you  assign depends on the guidelines and procedures within your organization. Default  assignments are provided for each alert. 8.4.1 Alert examples  8.4.2 Alert to monitor back-end capacity: Available Physical Space (%) Table 8-3 Event examples for IBM Flash System 9100 System Entity Resource Type Event FS9100 with FCM Array Usable capacity Available Physical Space <= nn% (* Example shown in “Alert to monitor  back-end capacity: Available Physical  Space (%)”) Pool Efficient Capacity Physical allocation >= nn% FS9100  other media Pool Usable Capacity Physical allocation >= nn% Chapter 8. Monitoring  303