🚀 go-pugleaf

In article <3752@rtech.rtech.com> daveb@rtech.UUCP (Dave Brower) writes:
> ... Some
>airline reservation systems are said to have huge farms of disk where
>only one or two tracks are used on the whole pack to avoid seeks, for
>instance.

No, I don't think so.

I did a consulting job for United Airlines' Apollo system a couple of
years ago, looking for architectures to break the 1000t/s limit.  We
looked at distributing transactions to many processors and disks,
etc., etc., but nothing quite so profligate at using only a couple of
tracks (or cyls) on a 1GB disk pack in order to minimize seeks.

On the *big iron* that UAL and other reservations systems use, the
operating systems (TPFII and MVS/ESA) implement very sophisticated
disk management algorithms, and in particular, implement elevator
seeking. 

With elevator seeking, disk I/O's in the queue are ordered in such a
way to minimize seek latency between I/O operations.  In an I/O-
intensive tp application with I/O's spread across multiple disk packs,
a good elevator scheduling scheme is all that's needed to get the
appropriate disk I/O bandwidth.

Makes for a good story, tho!

phil





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| Phil Fernandez              |             philf@metaphor.com               |
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