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Chapter 7. Copying Data from Arrays and from Volume Groups
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When disk drives are configured through the Logical Volume Manager for mirroring, you
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can use the Split Copy function to create a copy of a logical volume. You can then save
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that copy on a tape or other medium for backup purposes. When disk drives are
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configured as members of a RAID-1 or RAID-10 array, a similar function, called 3-Way
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Copy, is available. This chapter describes the 3-Way Copy function, and how it can be
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used. It does not describe the Split Copy function of the Logical Volume Manager.
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Note: The 3-Way Copy function is available only with adapter microcode level A000 or
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The 3-Way Copy procedure allows you to create a separate copy of an hdisk, of a
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complete volume group, or of part of a volume group. The copy is prepared on a
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separate disk drive for a RAID-1 array, or on several disk drives for a RAID-10 array.
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You cannot use the 3-Way Copy procedure for RAID-5 arrays, for RAID-0 arrays, or for
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non-RAID disk drives, whether or not they are configured for Logical Volume mirroring.
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When the copy has been prepared, and the copy operation is complete, the copy
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remains synchronized with the parent. It can be uncoupled later. The uncoupled copy is
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renamed from the original name so that it can be separately accessed after it is
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uncoupled.
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If the RAID-1 arrays or RAID-10 arrays are used as raw hdisks, you control the 3-Way
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Copy function from SMIT menus or from ssaraid commands. Facilities are provided that
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allow you to identify suitable candidate disk drives for the copy and to couple those disk
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drives to the parent array. By using SMIT menus or an ssaraid command, you can
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uncouple the copy from the parent array; the uncoupled array becomes a new hdisk.
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Before the copy is uncoupled, all fast-write data is destaged to the array. Data held in a
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system cache that has not yet been sent to the adapter must be flushed before the
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uncouple operation.
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If the RAID-1 or RAID-10 array is used to hold logical volumes, you can use the
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ssa_make_copy command to make and uncouple a copy of the complete logical
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volume group, or of part of a logical volume group. This command:
v Selects disk drives for the copy operation
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v Synchronizes data from system cache memory to the array
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v Copies the required logical volume group, logical volume, or file system to the copy
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disk drives
v Uncouples the copy disk drives from the parent array
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v Renames the volume group and logical volumes
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The complete procedure for synchronizing the data, copying to separate disk drives,
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and uncoupling the copy can therefore be done from a single command. You can use
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SMIT menus or ssaraid commands to copy and uncouple RAID-1 and RAID-10 arrays
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that hold logical volumes, as you do for raw hdisks. SMIT commands or ssaraid
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commands, however, operate only on whole hdisks. If you use these commands, you
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must ensure, in a separate operation, that all cached data in system memory has been
above.
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