Path: utzoo!utgpu!water!watmath!clyde!att!osu-cis!tut.cis.ohio-state.edu!mailrus!ames!lll-lcc!well!ewhac
From: ewhac@well.UUCP (Leo 'Bols Ewhac' Schwab)
Newsgroups: comp.sys.amiga.tech
Subject: Re: Fast File System for floppys ... how to.
Message-ID: <5968@well.UUCP>
Date: 15 May 88 22:23:11 GMT
References: <5256@cup.portal.com> <1056INFO@NDSUVM1>
Reply-To: ewhac@well.UUCP (Leo 'Bols Ewhac' Schwab)
Organization: onhigh!oracle
Lines: 40

In article <1056INFO@NDSUVM1> elg@killer.UUCP (Eric Green) writes:
>in article <5256@cup.portal.com>, doug-merritt@cup.portal.com says:
>> How about a little hotkey input handler that you bring up when you
>> want to pop a FFS diskette, that flushes buffers and tells you
>> when it's safe?
>>
>What I'm wondering about is -- since FFS is so unsafe on floppies,
>how can we trust our hard drives to it?
>
>That is, if there can be buffered data that hasn't been written to the disk in
>eons, then, how do I know when it's safe to turn off my hard drive based
>system?
>
	Slight misunderstanding there, due to less-than-optimal wording by
Doug Merritt.

	FFS currently does not know how to generate a DISKCHANGE signal
internally.  This means that if you mount FFS on to a floppy drive, when you
eject the disk, FFS will sit there and go, "Duhhh?"  This isn't so bad,
except that FFS will do the same thing when you insert a new floppy in the
drive.  Since FFS has no idea that you've changed volumes, FFS assumes that
the volume was never changed, and will write all over it based on now
invalid values.

	Note that there are no outstanding buffers waiting to be written to
the now-removed volume.  AmigaDOS does not hold on to buffers like UNIX.
Hence, removed volumes will always be consistent, provided you wait for the
little red light to go out and stay out.

	So, in order to safely change disks with FFS mounted on a floppy
drive, you have to say "DiskChange" on that drive.  Since hard disks are
typically fixed media, the inability to internally generate DISKCHANGED
isn't a major problem for FFS.  The only real losers in this scenario are
the people with Bernoulli-type drives.

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Leo L. Schwab -- The Guy in The Cape  ihnp4!pacbell -\
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