Hard Disks – What is Serial Storage Architecture?

Today’s huge databases and data intensive applications demand incredible amounts of storage, and transferring massive blocks of information requires technology that is robust, reliable and scaleable. Serial Storage Architecture ( SSA) is an IBM-developed interface for connecting storage devices, storage subsystems, servers and workstations in mission-critical PC server applications. However, by the start of 1999 it had failed to win major support, and appeared likely to lose out to the rival Fibre Channel standard.

SSA provides data protection for critical applications by helping to ensure that a single cable failure will not prevent access to data. All the components in a typical SSA subsystem are connected by bi-directional cabling. Data sent from the adapter can travel in either direction around the loop to its destination. SSA detects interruptions in the loop and automatically reconfigures the system to help maintain connection while a link is restored.

Up to 192 hot-swappable hard disk drives can be supported per system. Drives are available in 2.25 and 4.51GB capacities, and particular drives can be designated for use by an array in the event of hardware failure. Up to 32 separate RAID arrays can be supported per adapter, and arrays can be mirrored across servers to provide cost-effective protection for critical applications. Furthermore, arrays can be sited up to 25 metres apart – connected by thin, low-cost copper cables – allowing subsystems to be located in secure, convenient locations, far from the server itself.

With its inherent resiliency and ease of use, SSA is being increasingly deployed in server/RAID environments, where it is capable of providing for up to 80 MBps of data throughput, with sustained data rates as high as 60 MBps in non-RAID mode and 35 MBps in RAID mode.