I thought Escon was about 17 Mb/sec and the B11 drives were 9 Mb/sec.
True, but the 17MB/sec on the channel is the maximum instantaneous rate;
the max effective rate after channel turnarounds and CU-channel control
exchanges is rarely more than 14MB/sec, usually less.
On the tape, the max sustained rate is 9 MB/sec, but compression
effectively triples the data rate (on the average, compression ratios
vary) so the effective tape rate is around 27MB/sec. this is a good
argument for FICON channels on 3590 drives, to make the channel faster
than the tape.
On 3480/3490 drives, the control unit could handle only one data
transfer for one drive at a time (I think you could get one drive
transfering data into cache while another drive wrote data from cache).
Most configurations were dual control units so you could get double the
operations. The STK drives mostly had a CU per drive so you could get
as many transfers as you had tapes. As I recall, the 3590 supports
multiple concurrent transfers into cache and multiple transfers from
cache to drive, so much more parallelism.
--
Bruce A. Black
Senior Software Developer for FDR
Innovation Data Processing 973-890-7300
personal: [EMAIL PROTECTED]
sales info: [EMAIL PROTECTED]
tech support: [EMAIL PROTECTED]
web: www.innovationdp.fdr.com
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