> > I'm curious. One of the benefits touted, and true, about > Linux on zSeries > > vs. some other platform, is the zSeries' strength in I/O. > Is this still true > > with FCP attached SCSI DASD? Why would the zSeries drive > SCSI DASD better > > than Intel or Sun? > > John McKown > > Senior Systems Programmer
Basically you can attach more dasd space and have more simultaneous (NOT just concurrent) data transfers going on at the same time. The I/O advantage of the mainframe is that it usually has more paths (256 channels) to more devices(65,536) thus giving a lot more parallel I/O, not that any particular device is more efficient. If you have a lot threads active, more I/O can be done in parallel that most intel and other boxes. With 256 channels at say 12 MB/sec (shark) on , the total aggregate rate of the mainframe would be about 3 GB/sec. Obviously, that's limited by the 2 GB backend buss on the TREXX. Also, the theoretical limit with 65,536 devices, each with 32GB, would be something like 2 exobytes! (1024x1024xGB) (correct if I used the wrong prefix - its bigger than terabyte and petabyte). Adding SCSI/Fibre channel, the rates also increase, but the number of maximum channels is reduced. Also, the main frame typically has 2 processors dedicated to driving the devices (SAPs), so less "real cpu" is used for I/O. The other processors can continue to do other work while the SAPs are doing data transfer to the devices. Only after the data transfer is complete need the "real" processors be notified. Path selection, etc,etc, has been moved to these SAPS. The mainframes make dandy servers when you need access to a lot of data quickly. ===== Jim Sibley RHCT, Implementor of Linux on zSeries "Computer are useless.They can only give answers." Pablo Picasso __________________________________ Do you Yahoo!? Get better spam protection with Yahoo! Mail. http://antispam.yahoo.com/tools
