This concept of data management directly benefits clients by having multiple file systems that  ProtecTIER can work with at the same time. If your ProtecTIER repository enables backup  speeds of 2500 MBps or more, you need at least 32 file systems in your back-end storage for  ProtecTIER to work with.  If you aim for a medium performance solution, you can use fewer than 32 file systems. Again,  these assumptions are more general ones, and your individual system will be fine if these  assumptions are implemented according to your individual sizing and planning. All of the current-generation storage subsystems offer some sort of technology that adds an  additional layer of virtualization to the distribution of data across the storage.  On the IBM Storwize Family and SAN Volume Controller, this technology is called  extent  striping . If you create a VDisk with the  -vtype striped  parameter (which is the default), all  managed disks in the managed disk group are used to create the virtual disk. The striping is  at an extent level; one extent from each managed disk in the group is used. For example, a  managed disk group with 10 managed disks uses one extent from each managed disk, and  then it uses the 11th extent from the first managed disk. On DS8000, this technology is called  storage pool striping  (SPS) or  rotate extents . The  storage pool striping function stripes new volumes across all ranks of an extent pool. A similar  approach is also used with IBM Storwize Family and SAN Volume Controller. So what is the benefit of performing striping? What benefits do extent striping, rotate extents,  and so on, provide? These features provide the following primary enhancements: These striping features enable you to avoid “hot spots” in your storage, to allocate more  turning spindles of the storage to drive your workload, and to enable easy expansion of your  environment even for existing arrays and LUNs.  Because of the design method that ProtecTIER uses to write data to disk, ProtecTIER  prevents creating a higher load on a single array only, while others stay idle. ProtecTIER does  not benefit from automatic hot spot avoidance. ProtecTIER needs multiple LUNs to work with. Some of these LUNs are used to store the  metadata, which must be RAID 10 to drive the heavily random write I/O. Some of these LUNs  are used to store the user data, which must be RAID 6 or RAID 5 to drive the random read  I/O. ProtecTIER evenly distributes the load across the storage system, and across all of the  available LUNs.  ProtecTIER also uses a special method to extend the back-end storage during the  ProtecTIER repository expansion process. Depending on the amount of storage that you  want to add, you can add or extend metadata, add user data, or both. Depending on how the  initial deployment of ProtecTIER was done, increasing the metadata might be done by adding  104  IBM ProtecTIER Implementation and Best Practices Guide GLYPH<SM590000> You can extend your existing arrays relatively easily by adding more extents to the existing  pools (easy expansion). GLYPH<SM590000> This approach can increase performance with minimal operator effort (high performance). GLYPH<SM590000> The striped volume layout reduces workload skew in the system without requiring manual  tuning by a storage administrator (hot spots). 7.4 Smart storage subsystems