Workload considerations
This topic highlights some of the considerations to bear in mind when you decide what workload to place in the TS7700.
The TS7700 presents 3490 Tape Drive images. Any data that can reside on a 3480/3490/3590/3592 or cartridges from other vendors can reside on the TS7700. However, processing characteristics of workloads differ, so some data are more suited for the TS7700 than other data.
Throughput
Because the TS7700 has a finite bandwidth capability, as has any other device that is attached to a host system, plan for workloads that fit its capabilities.However, since the TS7700 possesses 4 Gb8 Gb FICON® channels and either Tape Volume Cache or TS7700 Cache, few workloads would not be suitable based on throughput.Drive concurrency
The TS7700 cluster appears to the host operating system as up to 496 3490E drives. If you have periods of time during the day when your tape processing jobs are limited by drive availability, the TS7700 can help your processing considerably. The design of the TS7700 cluster allows transparent access to multiple virtual volumes on the same stacked physical volume because access to the virtual volumes is solely through the TS7700 Cache. If you need access to more than one virtual volume on a physical volume, it is provided without requiring any user involvement, unlike some alternatives such as stacking by using job control language (JCL).Cartridge capacity utilization
One of the key benefits of the TS7700 is its ability to fully use the capacity of the 3592 Tape Cartridges independent of the data set sizes that are written. Another is the ability to manage that capacity effectively without host or user involvement. A virtual volume can contain up to 6.2926.21 GB of data (18.8778.63 GB assuming data compressibility of 3:1) using the extended virtual volume sizes.The actual size of a virtual volume is only the amount of data that is written by the host. If an application writes 20 MBs to a 4 GB volume, only the 20 MB is kept in the TS7700 Cache or on a physical volume in a TS7770 Tape Attach or TS7760 Tape Attach. Large data sets can gain little from the ability of the TS7700 to stack data, so you can decide to leave them on native 3590 or 3592 Tape Cartridges.
Volume caching
Often, one step of a job writes a tape volume and a subsequent step (or job) reads it. The TS7700 improves the efficiency of this process: As data is cached in the TS7700 Cache the rewind time, the robotics time, and load or thread times for the mount are effectively removed. When a job attempts to read a volume that is not in the TS7700 Cache, the virtual volume is recalled from a stacked physical volume back into the cache. When a recall is necessary, the time to access the data is greater than if the data were already in the cache. The size of the cache and the use of cache management policies can reduce the number of recalls. Too much recall activity can negatively affect overall throughput of the TS7700.Scratch mount times
When a program issues a scratch mount to write data, the TS7700 completes the mount request without having to recall the virtual volume into the cache. For workloads that create many tapes, this significantly reduces volume processing overhead times and improves batch window efficiencies.Scratch mount times are further reduced when the optimal scratch allocation assistance function is enabled. This function designates one or more clusters as preferred candidates for scratch mounts by using a Management Class construct defined from the TS7700 Management Interface. For more information, see the Optimal scratch allocation assistance topic in the Related information section.
Disaster recovery
The grid configuration of the TS7700 is a perfect integrated solution for your disaster recovery data. Multiple TS7700 Clusters can be separated over long distances and interconnected by using an IP infrastructure to provide for automatic data replication. Data that is written to a local TS7700 is accessible at the remote TS7700 as if it was created there. Flexible replication policies make it easy to tailor the replication of data to your business needs.Another disaster recovery solution is the Copy Export function. Copy Export allows a copy of selected virtual volumes that are written to the TS7700 to be removed and taken offsite.
For more information about disaster recovery configuration, see Configuring for disaster recovery. For more information about the Copy Export function, see Copy export overview.
Multifile volumes
If you currently stack multiple files onto volumes by using JCL constructs or some other method, the reason you are stacking is most likely to better use cartridge capacity. Automatic utilization of physical cartridge capacity is one of the primary attributes of the TS7700. Therefore, in many cases manual stacking of data sets onto volumes is no longer required. If you are planning a new application that would have used JCL to stack data sets onto a volume, the TS7700 makes this JCL step unnecessary. Multifile volumes moved to the TS7700 works without modification to the stacking. However, the TS7700 recalls the complete virtual volume to the TS7700 Cache if the volume is not in cache, rather than moving each file as you access it. Therefore, in some cases, it can be advantageous to allow the TS7700 do the stacking automatically for you. It can save you manual management overhead and in some cases, host CPU cycles, channel bandwidth, DASD space, or a combination of all.Interchange/offsite storage
As currently delivered, the TS7700 does not support a capability to remove a stacked volume to be used for interchange or offsite storage. Native 3490, 3590, or 3592 tapes are better suited for interchange or offsite storage. For disaster recovery offsite data storage, the TS7770 Tape Attach and the TS7760 Tape Attach models provide the Copy Export function.Grid network load balancing
For a TS7700 Grid link, the dynamic load balancing function calculates and stores the following information:- Instantaneous throughput
- Number of bytes queued to transfer
- Total number of jobs queued on both links
- Whether deferred copy throttling is enabled on the remote node
- Whether a new job will be throttled (is deferred or immediate)