Draft Document for Review February 7, 2020 3:15 pm 8464ch02_Architecture.fm function can be used for added resiliency or with the Copy Export function to provide a  secondary offsite physical copy for DR purposes. For more information about Copy Export,  see 2.3.14, “Copy Export function” on page 53. The second copy of the logical volume is created in a separate physical pool to ensure  physical cartridge separation. Control of Dual Copy is through the MC construct (see  “Management Classes window” on page 455). The second copy is created after the original  volume is pre-migrated.  Important:  When used for  Copy Export , ensure that reclamation in the secondary physical  volume pool is self-contained (the secondary volume pool reclaims onto itself) to keep  secondary pool cartridges isolated from the others. Otherwise, Copy Export DR  capabilities might be compromised. The second copy that is created through the Selective Dual Copy function is available only  when the primary volume cannot be recalled or is inaccessible. It cannot be accessed  separately, such as when the primary volume is being used by another operation. The second  copy provides an error path recovery backup if the primary volume is damaged or  inaccessible. Selective Dual Copy is defined in the TS7700T and includes the following characteristics: GLYPH<SM590000> The selective dual copy feature is enabled by the MC setting through the MI where you  define the secondary pool. GLYPH<SM590000> Secondary and primary pools can be intermixed: – A primary pool for one logical volume can be the secondary pool for another logical  volume unless the secondary pool is used as a Copy Export pool. – Multiple primary pools can use the same secondary pool. GLYPH<SM590000> At Rewind Unload (RUN) time or inbound copy complete, the secondary pool assignment  is determined and premigration of the logical volume is scheduled. The primary must first  be successfully premigrated before the secondary is queued for premigration. GLYPH<SM590000> The logical volume in disk cache is retained until both copies to back-end tape are  completed. 2.3 General TVC management in a stand-alone cluster  The TS7700 cluster manages logical volume data within the TVC cache. By using policy  settings and LI REQ settings, you can influence certain behaviors that are related to  managing data in TVC cache. For example, defining how data moves to back-end tape or  cloud, or defining how long to retain data that is associated with expired scratched volumes. 2.3.1 Basic Rules for TVC Management Cache Management can be summarized by the following rules: GLYPH<SM590000> The TS7700 emulates a 3490E tape of a specific size that is chosen through the DC  construct. However, the space that is used in the TVC is the number of bytes of data that is  written to the virtual volume after compression and after a minimal amount of TS7700  metadata is introduced. If a virtual volume is written to the physical tape or the cloud, it  uses only the space that is occupied by the compressed data and resulting metadata. Chapter 2. Architecture, components, and functional characteristics  39