Hybrid TS7700 Grid configurations

A hybrid TS7700 Grid is one that contains an intermix of one or more TS7700 tape-attach Clusters and one or more TS7700 disk-only Clusters that are configured together within the same grid.

The hybrid grid configuration is used for archival and data retention purposes where data consistency shifts from disk-only clusters (clusters that do not connect to a physical library) to clusters that do connect to a physical library. Data that is contained within any TS7700 Cluster can be accessed by any peer cluster, regardless of either cluster's connection to a physical library.

A hybrid TS7700 Grid can be configured by using between two and six TS7700 Clusters.

Five- or six- cluster hybrid

Five- and six-cluster hybrid grid configurations are supported by RPQ only. Possible configurations of five and six cluster grids include:

Two production sites each with two clusters, plus a one- or two-cluster disaster recovery site: Each production site contains one disk-only cluster combined with one cluster attached to a physical library. When part of a five-cluster grid, the disaster recovery site contains one cluster attached to a physical library. When part of a six-cluster grid, the disaster recovery site also contains a disk-only cluster.; Each production site writes and reads only to its local clusters and all data that is written within either production site is replicated to the adjacent cluster and all disaster recovery clusters.
One production site with three clusters, plus one disaster recovery site with three clusters: Each site contains two disk-only clusters and one cluster attached to a physical library. This configuration is available only with a six-cluster grid.; Data that is written to a production cluster is replicated to one adjacent cluster and to at least two disaster recovery clusters.

Figure 1. Example of a TS7720, TS7740, and TS7760 6-way hybrid Grid configuration

Figure 2. Example of a TS7720, TS7740, and TS7760 5-way hybrid Grid configuration

Four-cluster hybrid

There are two common configurations of a four-cluster grid:

Two disk-only production clusters, plus two remote clusters attached to physical libraries: Disk-only clusters are used for production data, while clusters attached to physical libraries are used for archival or disaster recovery purposes. Optimally, the clusters that are attached to physical libraries are at metro distances to separate long-term data from a single point of loss.; All clusters are configured for high availability. However, the production clusters are also configured for high cache hit rates. Long-term retention data migrates to the clusters attached to physical libraries. The copy export function can be used on these clusters to produce a second or third offsite copy of long-term retention data.
Identical production and remote configurations: One configuration is duplicated at multiple sites: one disk-only cluster combined with one cluster attached to a physical library. This provides a high-availability solution for both production and archival data centers, while distancing the clusters attached to physical libraries for disaster recovery purposes. All clusters are configured for high cache hit rates.

Figure 3. Example of a TS7720, TS7740, and TS7760 4-way hybrid Grid configuration

Three-cluster hybrid

One disk-only cluster is used for production, as is one of the clusters attached to a physical library. The other cluster that is attached to a physical library is used for archival or disaster recovery purposes. This solution is a high availability production configuration that also provides the benefits of high cache hit rates for recent data.

Figure 4. Example of a TS7720, TS7740, and TS7760 3-way hybrid Grid configuration

Two-cluster hybrid

One disk-only cluster is used for production, while one cluster attached to a physical library is used for archival or disaster recovery purposes. Copy export can be used to produce a second offsite copy of the long-term data that resides only in the cluster attached to a physical library.

Figure 5. Example of a TS7760 hybrid configuration

Table 1 summarizes the possible configurations of a hybrid TS7700 Grid.

Table 1. Hybrid grid configurations
Total clusters	Site A	Site B	Site C	Expectations
6	Production 1 disk-only cluster 1 library-attached cluster	Production 1 disk-only cluster 1 library-attached cluster	Backup 1 disk-only cluster 1 library-attached cluster	High availability at two sites. Remote access for volumes no longer in disk-only cache. Optimal cache hits of newer content at production sites. Copy export is optionally used to create offsite copies of long-term content.
6	Production and backup 2 disk-only clusters 1 library-attached cluster	Production and backup 2 disk-only clusters 1 library-attached cluster	No third site	High availability at both sites. Local access for volumes no longer in disk-only cache. Copy export is optionally used to create offsite copies of long-term content.
5	Production 1 disk-only cluster 1 library-attached cluster	Production 1 disk-only cluster 1 library-attached cluster	Backup 1 library-attached cluster	High availability at both sites. Local access for volumes no longer in disk-only cache. Optimal cache hits of newer content at production sites. Copy export is optionally used to create offsite copies of long-term content.
4	Production 2 disk-only clusters	Backup 2 library-attached clusters	No third site	High availability at both sites. Remote access for volumes no longer in disk-only cache. Optimal cache hits of newer content at the production site. Copy export is optionally used to create offsite copies of long-term content.
4	Production 1 disk-only cluster 1 library-attached cluster	Production or backup 1 disk-only cluster 1 library-attached cluster		High availability at both sites. Local access to volumes on tape. Second production site as backup. Optimal cache hits at both production and backup sites.
3	Production 1 disk-only cluster 1 library-attached cluster	Backup 1 library-attached cluster		High availability at the production site. Can require remote mount if local library-attached cluster is down and volume is not in cache. Optimal cache hits at the production site.
2	Production 1 disk-only cluster 1 library-attached cluster	No remote clusters		High availability for recently used volumes. Copy export is optionally used to create offsite copies of long-term content. Loss of cluster attached to physical library can prevent access to older volumes. For scheduled outages, a pre-removal of volumes from the disk-only cluster would be required to assure enough cache space is available.

Important: Copy policies must be set up correctly across the hybrid grid. Optimally, all volumes that are created on a disk-only cluster have a copy policy that creates a copy on one or more clusters attached to a physical library. Otherwise, the automatic removal cannot remove volumes from the disk-only cache, leading to the disk-only cache reaching its maximum capacity. If this happens, a manual intervention is required to reduce the volume use of the disk-only cluster.

TS7700 Clusters that attach to a physical library have a much higher total storage capacity than disk-only TS7700 Clusters. In a hybrid grid, a copy export from a cluster that is attached to a physical library can export all the contents of the library including any hybrid-migrated data that resides only on the TS7700 Clusters attached to a physical library. Therefore, when a complete failure occurs to a copy export parent site, it is possible that the copy exported volumes are the only source for the hybrid-migrated data. A recovery in this scenario can occur by initiating a disaster recovery process into a new TS7700 Cluster attached to a physical library by using the copy exported volumes. This allows the data to be merged back into the composite library and any preexisting TS7700 Clusters remain present with valid content. This disaster recovery approach, as opposed to a copy export recovery approach, does not require the recovery point to be a stand-alone TS7700 Cluster attached to a physical library.