> Please, no more internal DASD! Don't even mention it! > > I think I have worked with every 360/370/390 that had > internal dasd and every one of them became a disaster. > If not all of them at least a few more than I wanted to!
Sorry, but this is the way things are going at the low end. Below 80 MIPS the only 'new technology' solution available is emulation - see http://www.isham-research.com/low_end_mainframes.html No emulation product can currently attach external System/390 format disks - Fundamental and IBM are currently testing an ESCON card but it's likely to cost over $10k a pop. See BusTech and Polaris for other PCI/ESCON cards - prices very similar. External DASD have been tested on FLEX-ES - but 'post-emulation', i.e., the ECKD DASD is emulated by FLEX-ES and data stored in a Linux file - this file can be stored externally via an appropriate host bus adapter. I don't know what the demand for external DASD on emulation platforms will be. So far, the lack of it has not been a major issue. However inconvenient internal DASD may be when it comes time to upgrade them, there are serious performance benefits - especially to I/O intensive (e,g, VSE) workloads. See http://www.perfassoc.com/flex-es_io_performance_02.pdf for an example - it's not unusual for 18 MIPS emulated systems (running on a 1GHz Intel processor) to run two or three times as fast as on external DASD. -- Phil Payne http://www.isham-research.com +44 7785 302 803 +49 173 6242039
