Draft Document for Review December 5, 2019 4:33 pm 8456ch_Virtualization_Concepts.fm GLYPH<SM590000> For ESE volumes, several logical extents, which are designated as  auxiliary rank extents ,  are allocated to contain volume metadata. Figure 4-11 shows the extent layout in the DS8870 and earlier, for ESE volumes. In  addition to the reserved area, auxiliary 1 GB extents are also allocated to store metadata  for the ESE volumes. In the DS8900F and DS8880, all volumes use an improved metadata extent structure, similar  to what was previously used for ESE volumes. This unified extent structure greatly simplifies  the internal management of logical volumes and their metadata. No area is fixed and  reserved for volume metadata, and this capacity is added to the space that is available for  use. The metadata is allocated in the Storage Pool when volumes are created, and the space that  is used by metadata is referred to as the  Pool Overhead . Pool Overhead means that the  amount of space that can be provisioned (allocated) by volumes is variable and depends on  both the number of volumes and the logical capacity of these volumes. Tips:  The following characteristics apply to the DS8900: Figure 4-11 DS8870 extent space-efficient volumes For storage pools with large extents, metadata is also allocated as large extents (1 GiB for FB  pools or 1113 cylinder for CKD pools). Large extents that are allocated for metadata are  subdivided into 16 MiB subextents, which are also referred to as  metadata extents , for FB  volumes, or 21 cylinders for CKD. For extent pools with small extents, metadata extents are  also small extents. Sixty-four metadata subextents are in each large metadata extent for FB,  and 53 metadata subextents are in each large metadata extent for CKD.  For each FB volume that is provisioned (allocated), an initial 16 MiB metadata subextent or  metadata small extent is allocated, and an additional 16 MiB metadata subextent or metadata  small extent is allocated for every 10 GiB of provisioned (allocated) capacity or portion of  provisioned capacity. Chapter 4. Virtualization concepts  117 GLYPH<SM590000> Metadata is variable in size. Metadata is used only as logical volumes are defined. GLYPH<SM590000> The size of the metadata for a logical volume depends on the number and size of the  logical volumes that are being defined. GLYPH<SM590000> As volumes are defined, the metadata is immediately allocated and reduces the size of  the available user extents in the storage pool. GLYPH<SM590000> As you define new logical volumes, you must allow for the fact that this metadata space  continues to use user extent space.