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Dell EMC Solutions Enabler 9.2 SRDF Family CLI User Guide

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Pair devices using storage groups

The createpair operation uses the following logic to pair devices in storage groups:

  • R1s are paired to R2s of like sizes. Geometry Compatible Mode (GCM) is taken into account.

    SRDF detects whether GCM is set or can be set/unset on local and remote devices. Geometry Compatible Mode” on page 28 provides more information about GCM.

  • If the R2 is larger than R1, the device chosen to be the R2 is as close to the R1 size as possible.
  • Device pairs must be the same emulation:
    • CKD 3380 to CKD 3380
    • CKD 3390 to CKD 3390
    • AS400 512 to AS400 512
    • AS400 520 to AS400 520
    • FBA to FBA
  • FBA meta devices are paired as follows:
    • Concatenated metas are paired to concatenated metas and striped metas are paired to striped metas.
    • The number of members in the two metas must be the same.
    • The stripe size of the two metas must be the same.
    • Thin-to-thin pairs are created before thin-to-thick pairs.
    • Thick-to-thick pairs are created before thin-to-thick pairs.
NOTE:If any of the devices in the two storage groups cannot be paired using these rules, the createpair operation fails.

Example

In the following example, storage group localSG includes 4 devices: 

---------------------------------------------------------
Sym                               Device             Cap
Dev     Pdev Name                 Config     Sts     (MB)
---------------------------------------------------------
000A0   N/A                       TDEV       RW      3278
000A1   N/A                       TDEV       RW      1875
000B1   N/A                       TDEV       RW      4125
000C1   N/A                       TDEV       RW      3278

The remote storage group remoteSG also has 4 devices: 

---------------------------------------------------------
Sym Device Cap
Dev Pdev Name Config Sts (MB)
---------------------------------------------------------
00030    N/A                       TDEV      RW      1877
00031    N/A                       TDEV      RW      4125
00050    N/A                       TDEV      RW      3278
00061    N/A                       TDEV      RW      4125

The createpair -type r1 operation pairs the devices in the localSG group with devices in the remoteSG group:

symrdf createpair -sid 123 -rdfg 250 -sg localSG -type r1 -remote_sg remoteSG

After the operation, pairings are:

Table 1. Device pairs in storage groups
Local storage group Remote storage group
Device name Device size Device name Device size
000A0 3278 MB 00050 3278 MB
000A1 1875 MB 00030 1875 MB
000B1 4125 MB 00031 4125 MB
000C1 3278 MB 00061 3278 MB

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