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Serial Storage Architecture (SSA) was a serial transport protocol used to attachdisk drives toserver computers. It was developed byIBM employeeIan Judd in 1990 to providedata redundancy for critical applications. SSA was deployed in server RAID environments, where it was capable of providing for up to 80 MB/s of data throughput, with sustained data rates as high as 60 MB/s in non-RAID mode and 35 MB/s in RAID mode.
SSA was promoted as an open standard by the SSA Industry Association, unlike its predecessor, the first generation Serial Disk Subsystem.[1] A number of vendors including IBM,Pathlight Technology and Vicom Systems produced products based on SSA. It was also adopted as anAmerican National Standards Institute (ANSI) X3T10.1 standard. SSA devices are logicallySCSI devices and conform to all of theSCSI command protocols.
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SSA was invented byIan Judd ofIBM in 1990. IBM produced a number of successful products based upon this standard before it was overtaken by the more widely adoptedFibre Channel protocol.
All the components in a typical SSA subsystem are connected by bi-directional cabling. Data sent from the adaptor 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 192hot swappable hard disk drives can be supported per system. Drives can be designated for use by an array in the event of hardware failure. Up to 32 separateRAID arrays can be supported per adaptor, and arrays can be mirrored across servers to provide cost-effective protection for critical applications. Arrays are connected by thin and inexpensive copper cables situated up to 25 metres apart, allowing subsystems to be located in secure, convenient locations, far from the server itself.
The copper cables used in SSA configurations are round bundles of two or four twisted pairs, up to 25 metres long and terminated with 9-pinmicro-D connectors. Impedances are 75 ohm single-ended, and 150 ohm differential. For longer-distance connections, it is possible to usefiber-optic cables up to 10 km (6 mi) in length. Signals aredifferential TTL. The transmission capacity is 20 megabytes per second in each direction per channel, with up to two channels per cable. The transport layer protocol isnon-return-to-zero, with8B/10B encoding (10 bits per character). Higher protocol layers were based on theSCSI-3 standard.
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Interfaces are listed by their speed in the (roughly) ascending order, so the interface at the end of each section should be the fastest.  Category | |