3956-XSB IBM TS7770 Cache Drawer

The IBM 3956-XSB is the TS7770 Cache Drawer (also called the cache module or cache expansion enclosure) for the IBM TS7770 virtual tape system. It acts as the expansion unit for the TS7770 Cache Controller 3956-CSB, and the two together form the TS7770 cache. The TS7770 pairs this cache with the 3957-VED server.

The XSB is a self-contained 2U enclosure that mounts in the 3952 Tape Frame. It holds twelve 3.5-inch NL-SAS 7.2K DDMs, each with a raw capacity of 10 TB (9.09 TiB), arranged as a distributed RAID (DRAID) with two rebuild areas equivalent to the capacity of two drives. Two AC power supplies with embedded cooling units are built in. A CSB controller supports only XSB drawers that contain the same size of drives as the CSB.

A 3956-CSB controller and up to nine attached 3956-XSB drawers form a string, with the controller at the head. A single TS7770 can have up to five strings, one in the base frame and four in the expansion frames. Cache enclosures ship from manufacturing in pairs, and a minimum configuration is one CSB with one XSB.

The CSB and XSB support encryption, including cryptographic erase and internal or external key management, and the drawers must be encryption-enabled when they ship because encryption cannot be enabled retroactively on a TS7770. IBM feature codes for the drawer are FC 5664 (plant installation of the 3956-XSB), FC 5665 (field install, which needs field merge feature 9355 on the cache module order), FC 9354 (plant install XSB) and FC 7119 (120 TB SAS storage). The TS7760 generation uses the 3956-XSA drawer. IBM made the 3956-XSB generally available on 22 November 2019.