Re: Some very thought-provoking ideas about OS architecture.

Mikulas Patocka (mikulas@artax.karlin.mff.cuni.cz)
Mon, 21 Jun 1999 11:49:57 +0200 (CEST)

> Here's another: All disk I/O is huge sequential BLTs done as part of
> checkpoint operations. You can actually use close to 100% of your
> controller's bandwidth, as opposed to the 30%-50% typical for
> explicit-I/O operating systems that are doing seeks a lot of the time.
> This means the maximum I/O throughput the OS can handle effectively
> more than doubles. With simpler code. You could even afford the time
> to verify each checkpoint write...

I believe that you get 100% write throughput, but in many systems read
requests are much more frequent than writes. I'd be insterested how good
is read performance. Wouldn't your data get too fragmented? If you
hadn't ported any applications to Eros yet, I wonder if you get good read
performance in real enviroment.

> Here's a third: Had a crash or power-out? On reboot, the system
> simply picks up pointers to the last checkpointed state. Your OS, and
> all your applications, are back in thirty seconds. No fscks, ever
> again!

I don't think it is really so important. If system crashes, something is
bad anyway, and you should cure the causation (fix bugs), not the
consequence (do quick recovery).
Power fault is another case, but I think it really doesn't matter if
system is down for 3 hours because of power fault or 3 hours and 10
minutes because of power fault and fsck.

Mikulas Patocka

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