Dual accessors and integrated service bays
When an optional second accessor is installed, the TS4500 tape library features high availability (HA), which enhances library performance. The extra accessor enables the library to operate without disruption if any component of one accessor fails. The integrated service bays reduce unusable service space by 40% compared to the TS3500 service bays. The default Maximum Capacity setting of the Elastic Capacity feature eliminates the remaining unusable service space.
If the library is installed with the optional second accessor, cartridge mount performance is also optimized. (A "mount" occurs when the accessor removes a cartridge from a drive, returns it to its storage slot, collects another cartridge from a random storage slot, moves it, and loads it into the drive.) The second accessor is part of feature code 1442.
When dual accessors are installed and an attached host issues a command for cartridge movement, the library automatically determines which accessor to mount cartridge in the most timely manner. Depending on the settings, if the library's primary accessor fails, the second accessor assumes control and eliminates system outage or the need for operator immediate intervention.
If you already have an installed TS4500 tape library and you want to add a second accessor, your IBM® service representative can add the accessor. Converting from a single accessor to a dual accessor disrupts the operations of the library.
The second accessor ships inside a Dx5 or Sx5 frame. You can place that frame anywhere in the library string. However, the B accessor is always installed as the right-most accessor.
Dual Accessor Settings
You have three options to choose from. Each option changes the zones within which each accessor operates.
Dual activeBoth accessors are online and active, and fulfill requests for media cartridges that fall within each accessor's preferred zone. In this option, the library is divided into two equally sized zones. While both accessors are active, the A accessor services the left zone and the B accessor services the right.
Accessor A OnlyOnly the A accessor is active and fulfills requests for media. The B accessor is online but parked in Service Bay-B. If the A accessor goes down, then the B accessor becomes active. In this option, the preferred zone for the A accessor includes the entire library with the exception of the area for Service Bay-B.
Accessor B OnlyOnly the B accessor is active and fulfills requests for media. The A accessor is online but parked in Service Bay-A. If the B accessor goes down, then the A accessor becomes active. In this option, the preferred zone for the B accessor includes the entire library with the exception of the area for Service Bay-A.
Service bays
Accessors are serviced through the side doors at the ends of the library. All front doors remain closed during accessor service, eliminating the need for dedicated service bay frames.
As you view the library from the front, Service Bay A is in the leftmost frame and it spans columns 3 - 8. Service Bay-A is where the A accessor moves to when it is placed in service. Service Bay-B is in the rightmost frame and it spans columns 5 - 10. Service Bay-B is where the B accessor moves to when it is placed in service. Integrated service bays reduce the number of unused storage columns in a dual accessor library from 22 to 14. While an accessor is in service, the media columns in that area are not available to the second accessor.
In frame one, the location of the I/O stations fall within the service bay area. Therefore, only Dx5 frames without the I/O station and Sx5 frames are supported as frame one in a dual accessor configuration. The rightmost frame can be an Lx5, Dx5, or Sx5 model.