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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. 

## 8.4.1 Alert examples 

Table 8-3 shows alerts for IBM FlashSystem 9100 systems based on Array or Pool level. 

<img src='content_image/994071.jpg'>

Other alerts are possible as well, but generally % alerts are best suited, as the alert definition applies to all pool in a storage system. 

## 8.4.2 Alert to monitor back-end capacity: Available Physical Space (%) 

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. 

