Draft Document for Review February 7, 2020 3:15 pm 8464ch02_Architecture.fm 2.4.23 TVC management for disk-only TS7700 clusters in a multi-cluster grid Enhanced Removal Policies Disk-only TS7700 clusters in a grid feature several unique options for cache management.  The Enhanced Volume Removal Policy provides tuning capabilities in grid configurations  where one or more disk only TS7700D clusters are present. Traditionally, other TS7700T or  TS7700C clusters also exist which have a much larger available capacity. Enhanced removal  policy provides a method to retain only certain workloads within the smaller capacity TS7700  solutions as data ages. Because the TS7700D has a maximum capacity (the size of its TVC), after this cache fills, the  Volume Removal Policy enables logical volumes to be automatically removed from this  TS7700D TVC while a copy is retained within one or more peer clusters in the grid. When  coupled with copy policies, TS7700D Enhanced Removal Policies provide various automatic  data migration functions between the TS7700 clusters within the grid. This is also true for a  TS7700T/TS7700C CP0. In addition, when the automatic removal is run, it implies an override to the current Copy  Consistency Policy in place, which results in a lowered number of consistency points  compared with the original configuration that is defined by the user. When the automatic removal starts, all volumes in scratch categories are removed first  because these volumes are assumed to be unnecessary. To account for any mistake where  private volumes are returned to scratch, these volumes must meet the same copy count  criteria in a grid as the private volumes. The pinning option and minimum duration time  criteria that are described next are ignored for scratch (Fast Ready) volumes.  To ensure that data always is in a TS7700D or CP0 for at least a minimal amount of time, a  volume retention time can be associated with each removal policy. This  volume retention time  (in hours) enables volumes to remain in a TVC for a certain time before the volume becomes  a candidate for removal. The time varies 0 - 65,536 hours. A volume retention time of zero  assumes no minimal requirement.  In addition to the volume retention time, the following policies are available for each volume in  a TS7700 CP0: GLYPH<SM590000> Pinned  GLYPH<SM590000> Prefer Remove: When Space is Needed Group 0 (LRU) – The available free space on the cluste r has fallen below the removal threshold. The copy of the volume is never removed from this cluster. No volume retention time is  applicable and it is implied as infinite. After a pinned volume is moved to scratch, it  becomes a priority candidate for removal similar to the next two policies. This policy must  be used cautiously to prevent cache overruns. The copy of a private volume is removed if the following conditions exist: – An appropriate number of copies exist on peer clusters. – The pinning duration (in number of hours) has elapsed since the last access or  creation.  The order in which volumes are removed under this policy is based on their LRU access  times. Volumes in Group 0 are removed before the removal of volumes in Group 1, except  for any volumes in scratch categories, which are always removed first. Archive and backup  data can be a good candidate for this removal group because it is not likely accessed after  it is written. Chapter 2. Architecture, components, and functional characteristics  79