8464ch04_Planning.fm Draft Document for Review February 7, 2020 3:15 pm 4.4.2 Virtual volumes Size of virtual volumes Determine the number of virtual volumes that are required to handle the workload that you  are planning for the TS7700. The default number of logical volumes that is supported is  1,000,000. You can add support for more logical volumes in 200,000 volume increments  (FC5270), up to a total of 4,000,000 logical volumes. Tip:  For 3957-V06/VEA, the maximum is 2,000,000 virtual volumes, which also is the limit  for the overall grid that contains clusters that correspond to one of those models. The TS7700 supports logical WORM (LWORM) volumes. Consider the size of your logical  volumes, the number of scratch volumes you need per day, the time that is required for  return-to-scratch processing, how often scratch processing is run, and whether you need to  define LWORM volumes. The TS7700 supports logical volumes with maximum sizes of 400, 800, 1000, 2000, 4000,  6000, and 25,000 mebibytes (MiB), although effective sizes can be larger if data is  compressed. For example, if your data compresses with a 3:1 ratio, the effective maximum  logical volume size for a 6000 MiB logical volume is 18,000 MiB.  Depending on the virtual volume sizes that you choose, you might see the number of volumes  that are required to store your data grow or shrink, depending on the media size from which  you are converting. If you have data sets that fill native 3590 volumes, even with 6000 MiB  virtual volumes, you need more TS7700 virtual volumes to store the data, which is stored as  multivolume data sets.  The 400 MiB cartridge storage tape (CST)-emulated cartridges or 800 MiB with emulated  enhanced capacity cartridge system tape (ECCST)-emulated cartridges are the two types  you can specify when adding volumes to the TS7700. You can use these sizes directly, or use  policy management to override them to provide for the 1000, 2000, 4000, 6000, or  25,000 MiB sizes.  A virtual volume size can be set by VOLSER, and can change dynamically by using the  DFSMS DC storage construct when a job requires a scratch volume or writes from the  beginning of tape (BOT). The amount of data that is copied to the stacked cartridge is only the  amount of data that was written to a logical volume. The choice between all available virtual  volume sizes does not affect the real space that is used in the TS7700 cache or the stacked  volume.  In general, unless you have a special need for CST emulation (400 MiB), specify the ECCST  media type when you insert volumes in the TS7700. In planning for the number of logical volumes that is needed, first determine the number of  private volumes that make up the current workload that you are migrating. One way to  determine this number is by looking at the amount of data on your current volumes and then  matching that figure to the supported logical volume sizes. Match the volume sizes,  accounting for the compressibility of your data. If you do not know the average ratio, use the  conservative value of 2:1.  If you choose to use only the 800 MiB volume size, the total number that is needed might  increase depending on whether current volumes that contain more than 800 MiB compressed  need to expand to a multivolume set. Consider that fact when planning the number of logical  volumes required. Consider the use of smaller volumes for applications, such as DFSMShsm  and larger volumes for backup and full volume memory dumps. Chapter 4. Preinstallation planning and sizing  177