Draft Document for Review February 7, 2020 3:15 pm 8464ch08_Migrate.fm Single-file format, as used by DFSMShsm, reduces I/O and system serialization because only  one label is required for each connected set (as opposed to multiple file format tapes that  require a label for each data set). The standard-label tape data set that is associated with the  connected set can span up to the allocation limit of 255 tapes. This standard-label tape data  set is called the  DFSMShsm tape data set . Each user data set is written in 16 K logical blocks  to the DFSMShsm tape data set. DFSMShsm-supported data set sizes Important:  A single DFSMShsm user data set can span up to 40 tapes (with z/OS V2R1,  this limit is now 254). This limit is for migration, backup, and recycle. After DFSMShsm writes a user data set to tape, it checks the volume count for the  DFSMShsm tape data set. If the volume count is greater than 215, the DFSMShsm tape data  set is closed, and the currently mounted tape is marked full and is de-allocated.  The number 215 is used so that a data set spanning 40 tapes fits within the 255-volume  allocation limit. DFSMShsm selects another tape, and then starts a different DFSMShsm tape  data set. Data set spanning can be reduced by using the  SETSYS TAPESPANSIZE  command. The TS7700 supports logical volume sizes of 400, 800, 1000, 2000, 4000, 6000, and  25000 MiB. In z/OS V1.13, with a maximum of 40 volumes that are supported and assuming  DFSMShsm and large logical volumes 800 MiB x 2.5 x 40 = 80000 MiB 800 MiB x 2.5 x 254 = 508000 MiB 6000 MiB x 2.5 x 40 = 600000 MiB a compression ratio of 2.5:1, the maximum user data set size for 800 MiB volumes is 80 GiB: In z/OS V2.1 and higher, the limit is 254 volumes for HSM user data sets, so the maximum  user data set becomes 508,000 MiB: Assume that you have a large data set of 300 GiB. This data set does not fit on 40 volumes of  800 MiB each, but it can fit on 6000 MiB large virtual volumes, as shown in the following  example: However, in z/OS V2.1 and higher, this data set can fit on 800 MiB volumes. Any single user  data set larger than 3.81 TiB at z/OS 1.13 or 15.875 TiB in z/OS 2.1 and higher is a candidate  for native 3592 tape drives. Assuming a compression rate of 2.5:1, they might not fit onto the  supported number of volumes. In this case, consider the use of native 3592-E06 (TS1130) or  3592-E07 (TS1140) tape drives rather than TS7700. IDCAMS DCOLLECT BACKUPDATA  can be used to determine the maximum size of backed-up data  sets in DFSMShsm inventory.  MIGRATEDATA  can be used to determine the maximum size of  migrated data sets in DFSMShsm inventory. Chapter 8. Migration  319