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Note:  If thin provisioning is used, the metadata is allocated for the entire volume (effective, virtual capacity) when the volume is created not when extents are used. 

## CKD Thin Provisioning 

Thin Provisioning is also possible with CKD volumes. See IBM DS8880 Thin Provisioning (Updated for Release 8.5) , REDP-5343, and check for APARs that are needed for certain z/OS versions. 

## Extent space efficient capacity controls for thin provisioning 

Use of thin provisioning can affect the amount of storage capacity that you choose to order. 

Use ESE capacity controls to allocate storage correctly. 

With the mixture of thin-provisioned (ESE) and fully provisioned (non-ESE) volumes in an extent pool, a method is needed to dedicate part of the extent-pool storage capacity for ESE user data usage, and to limit the ESE user data usage within the extent pool. 

Also, you need to detect when the available storage space within the extent pool for ESE volumes is running out of space. 

ESE capacity controls provide extent pool attributes to limit the maximum extent pool storage that is available for ESE user data usage. They also guarantee that a proportion of the extent pool storage will be available for ESE user data usage. 

The following controls are available to limit the use of extents in an extent pool: 

GLYPH<SM590000> Reserve capacity in an extent pool by enabling the extent pool limit function with the chextpool -extentlimit enable -limit extent_limit_percentage pool_ID command. 

GLYPH<SM590000> You can reserve space for the sole use of ESE volumes by creating a repository with the mksestg -repcap capacity pool_id  command. 

Figure 4-13 shows the areas in an extent pool. 

<img src='content_image/983084.jpg'>

