IBM Corp’s disk business is in big trouble – again, Hesh Wiener reports from New York. The 3990-6 disk controller, used with Ramac 9391/9392 RAID 5 disk subsystems, appears to be incapable of providing support for more than 180Gb of disk capacity – or two full 9391 racks at 90Gb each. Even when users have less than 180Gb, 3990-6/Ramac performance has been so poor that IBM has given a number of shops extra cache memory. It appears that 3990-6 controllers with 128Mb of cache do not deliver satisfactory response times: IBM has very quietly doubled the cache on these at no charge. Similar performance problems may affect the Ramac 9394/9395 models, which have built-in cache controllers: these models do not have all the features of a 3990-6 but are generally held to be no faster, and it is said that IBM has at times bid a 512Mb 3990-6 at the price of a 128Mb controller to hold onto users that might otherwise choose an EMC Corp Symmetrix disk subsystem. The extra cache can raise performance of a 3990-6/Ramac subsystem to satisfactory levels with current Ramac disks, but until IBM can ship a signficantly faster controller, it will have to delay providing the next generation of Ramac disk modules, which were initially expected to use 4Gb drives in place of the current 2Gb ones, forcing IBM to go straight to 8Mb 3.5 drives. (C) 1995 Technology News Ltd. A detailed article on the subject of Ramac will appear in the April 1995 edition of Infoperspectives International.
