Pair volume requirements and recommendations

The following is provided to help you prepare TrueCopy volumes:

• A volume can be assigned to only one pair.
• Logical units on the primary and secondary storage systems must be defined and formatted prior to pairing.
• The P-VOL and S-VOL must have the same capacity.
• TrueCopy requires a one-to-one relationship between the P-VOL and S-VOL. The P-VOL cannot be copied to more than one S-VOL, and an S-VOL cannot have more than one P-VOL.
• Logical Unit (LU) types
  • (VSP 5000 series) TrueCopy supports the basic LU types that can be configured on VSP G1x00 and VSP F1500 (for example, OPEN-3, OPEN-E, OPEN-8, OPEN-9, OPEN-L, and OPEN-V).
  • Pair volumes must consist of LUs of the same type and capacity (for example, OPEN-3 to OPEN-3).
  • (VSP 5000 series) Multi-platform volumes (for example, 3390-3A/B/C) cannot be assigned to pairs. Contact customer support for the latest information about supported devices for your platform.
• The LUN paths must be defined for both P-VOL and S-VOL, or both P-VOL and S-VOL must be defined as namespaces on the NVM subsystems to which NVM subsystem ports have been added.
• TrueCopy operates on volumes rather than on files. Multi-volume files require special attention. For complete duplication and recovery of a multi-volume file (for example, a large database file that spans several volumes), make sure that all volumes of the file are copied to TrueCopy S-VOLs.
• TrueCopy pair volumes can be shared with non-TrueCopy Hitachi software products. For details, see Sharing TrueCopy volumes.
• TrueCopy supports Virtual LVI/LUN. This allows you to configure LUs that are smaller than fixed-size LUs. When custom-size LUs are assigned to a TrueCopy pair, the S-VOL must have the same capacity as the P-VOL.

  TC pair might not be created when the PPRC multi-target function of TrueCopy for Mainframe. For details, see the Hitachi TrueCopy® for Mainframe User Guide.

• Before creating multiple pairs during the Create Pairs operation, make sure to set up S-VOL LUNs to allow the system to correctly match them to P-VOLs.

  In HDvM - SN, even though you select multiple volumes as P-VOLs, you specify just one S-VOL. The system automatically assigns subsequent secondary system LUs as S-VOLs based on the option you specify for Selection Type. These are the options:

  • Interval: The interval you specify will be skipped between LU numbers in the secondary system.

    For example, suppose you specify LU 01 as the initial (base) S-VOL, and specify 3 for Interval. This results in secondary system LU 04 being assigned to the next P-VOL, 07 assigned to the subsequent P-VOL, and so on. To use Interval, you set up secondary system LU numbers according to the interval between them.

  • Relative Primary Volume. The difference is calculated between the LUN numbers of two successive P-VOLs. S-VOLs are assigned according to the closest LUN number.

    For example, if the LUN numbers of three P-VOLs are 1, 5, and 6 and you set LUN numbers for the initial S-VOL (Base Secondary Volume) at 2, the LUN numbers of the three S-VOLs will be set at 2, 6, and 7, respectively.

• Because the contents of the P-VOL and S-VOL are identical, the S-VOL can be considered a duplicate of the P-VOL. Because the host operating system does not allow duplicate volumes, the host system administrator must take precautions to prevent system problems related to duplicate volumes. You must define the S-VOLs so they do not auto mount or come online to the same host at the same time as the P-VOLs.

  TrueCopy does not allow the S-VOL to be online (except when the pair is split). If the S-VOL is online, the TrueCopy paircreate operation will fail.

  CAUTION:
  When P-VOLs and S-VOLs are connected to the same hosts, define the S-VOLs to remain offline even after the hosts are restarted. If a pair is released and a host is subsequently restarted, the S-VOL should remain offline to prevent errors due to duplicate volumes.