Re: [9fans] fs (config) questions

[forsyth@caldo.demon.co.uk]

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each time i've considered that question (each time
i've configured a new file server) i've eventually decided
in favour of using the pseudo-worm driver.
it isn't more resilient in the face of certain crashes
but it might be slightly more likely to detect an inconsistency
sooner rather than later (or at least more cleanly).
i could be wrong but i suspect a few supporting commands rely on getting
a read error for blocks not yet written (cwcmd prchain might be one).

i'm glad i did keep the bitmap the last time, for another reason.
the written-block bitmap also turned out to be quite
useful when copying the existing structure to a real
worm jukebox, since it said which blocks had actually
been written, and helped to set precise limits for the copy.

another useful hint when copying a
pseudo-worm to a new file server with a real jukebox
and a new set of cache discs with a different structure is to do
	cwcmd savecache
on the file server, and {disk/exsort -w} before
starting the copy.  that way, cwcmd loadcache
will reload the cache on the new file server
with much less jukebox activity (and that's an understatement).


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From: "Russ Cox" <rsc@plan9.bell-labs.com>
To: 9fans@cse.psu.edu
Subject: Re: [9fans] fs (config) questions
Date: Fri, 13 Apr 2001 14:08:38 -0400
Message-ID: <200104131808.OAA20972@smtp2.fas.harvard.edu>

	yes it is possible, but not quite that easy (yet).  i've done it several times,
	using a specially-modified file server kernel to initialise the
	bitmap for the pseudo-worm area
	(after that the normal code is happy to include and write to the extended space).

is there a reason to use the pseudo-worm driver at all?
as far as i could tell, it's just making sure that blocks don't
get written twice.  that's important, i guess, assuming the
cached worm driver is debugged, i'd expect to be
able to use `cw1w2' to the same effect as `cw1fw2' except
that the former doesn't have the bitmap and thus can be
lifted from one disk onto another without a special kernel.

am i missing something?  (probably.)

russ