Path: utzoo!attcan!uunet!lll-winken!lll-tis!helios.ee.lbl.gov!pasteur!agate!bionet!apple!bloom-beacon!bu-cs!encore!bzs@xenna
From: bzs@xenna (Barry Shein)
Newsgroups: comp.sys.next
Subject: Re: Paging and swapping to a removable disk?
Message-ID: <3924@encore.UUCP>
Date: 19 Oct 88 19:47:00 GMT
References: <12670001@eecs.nwu.edu>
Sender: news@encore.UUCP
Reply-To: bzs@xenna (Barry Shein)
Organization: Encore Computer Corp
Lines: 27
In-reply-to: gore@eecs.nwu.edu (Jacob Gore)

>Does Mach (on a NeXT, at any rate) do memory swapping to disk?
>If so, what does it use for the swap area at times when the laser disk is out?
>(Or are you guaranteed that no page faults or process swapping will occur
>while you've got nothing in that drive???)
>
>Jacob Gore				Gore@EECS.NWU.Edu

I'll stick my neck out and say that I don't believe that you'll be
able to remove the optical disk if that's what you're paging and
swapping to (if you have a winch then it's a whole different matter.)

I would guess you'd have to bring the system down to a halt to change
disks. Even if it could stop everything (eg. treat it like Sun does a
netdisk when a server goes down) what could it do when you pop in a
different disk? It can't start paging/swapping again, the data on this
new disk is all wrong, so you'd be hung anyhow, better to reboot.

Reminiscent of Macs with floppies only where you keep a system folder
on every application's floppy, only I doubt that's the idea here
either.

It would be interesting to hear what, if anything, NeXT has done in
regards to this. My guess is nothing (ie. to change optical disks you
bring the system down, change, reboot, unless you have a winch to run
the system off of, or possibly some sort of NFS protocol to direct all
swapping/paging to a server.)

	-Barry Shein, ||Encore||