Considerations for creating ShadowImage pairs

ShadowImage User Guide

Part Number

Keep the following considerations in mind when creating SI pairs:

  • The P-VOL and S-VOL must be the same size in blocks. If the capacity is displayed in GB or TB, a small difference between P-VOL and S-VOL capacity might not be displayed. To view the capacity in blocks, click Options > Capacity Unit > block in the Logical Devices window.
  • If your storage system has encryption BEDs, you can copy an encrypted volume to an unencrypted volume. There is no guard logic to enforce copying encrypted P-VOLs to only encrypted S-VOLs. Unless there is a specific reason for the data to become unencrypted, make sure you maintain the encryption by using only encrypted S-VOLs.
  • The larger the volume capacity, the longer the time from creation of a pair until it transitions to PAIR status. For virtual volumes, the more pages allocated to a virtual volume, the longer the time from pair creation to PAIR status. Even when no pages are allocated to a virtual volume, if the volume capacity is 60 TB, it takes at least 30 minutes until the status changes to PAIR after pair creation. If the volume capacity is 256 TB, it takes at least an hour.
  • The value of the T10 PI attribute must be the same for the P-VOL and S-VOL.
  • When you simultaneously create an L1 pair and an L2 pair, if you select Quick Split or Steady Split for Split Type in HDvM - SN or specify the -split command in CCI, the L2 pair split begins before the L1 pair status changes to PSUS. Because of this, the operation might fail.
  • After creating a SI pair, if the number of pairs displayed in the summary section and the number of listed pairs in the HDvM - SN window are different, the configuration might be changed. Wait a while, and then select File > Refresh All to update the configuration information.
  • Initial copy is performed with a maximum of 24 multiplicities (number of jobs for which concurrent copy can be performed) for each pair. However, if Steady Split or Quick Split is set as the split type, the multiplicity is set to 1. Because of this, the processing time becomes longer than when Non Split is set as the split type. In the Edit Local Replica Options window, if Quick/Steady Split Multiplexing (ShadowImage/ShadowImage for Mainframe) option is enabled, the maximum number of multiplexing becomes 24 even when Steady Split or Quick Split is set as the split type.
  • If only the P-VOL capacity of an L1 pair has been expanded, an L2 pair cannot be created. Make sure to create the L2 pair after expanding all of the volume capacity used in the pairs.