From mboxrd@z Thu Jan  1 00:00:00 1970
To: 9fans@cse.psu.edu
Subject: Re: [9fans] (no subject)
From: Fco.J.Ballesteros <nemo@gsyc.escet.urjc.es>
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Date: Tue,  4 Sep 2001 15:30:36 +0200
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That's cool. BTW, I'm just wondering...

Would a system crash while doing a (mirrowed) dump
corrupt both disks at the same time?

While I was trying to use a couple of ide disks to
survive disk crashes, I thought it would be better
not to use a real mirror because a crash at a bad
moment could perhaps leave the cached worm unusable.
(I had a crash while doing a dump on a cached worm and
 the cached worm became unusable).

Am I missing something? A recover procedure I don't
know of? Or perhaps some code in the mirror device tries
to deal with that?

Another question I have is can you rebuild your mirror
device just by raw copying of one disk into another?






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From: geoff@collyer.net
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List-Id: Fans of the OS Plan 9 from Bell Labs <9fans.cse.psu.edu>
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Date: Tue, 4 Sep 2001 05:08:33 -0700

I've fixed some bugs in the IDE file server (some latent, some new in
the IDE code) and added a mirroring device.  I've tested it, it works
and later today it will be my main file server.  The mirroring device
is really very little code; the file server's elegant design is
largely responsible for this.  Doing a dump of 457121 4K blocks from a
cache device on h0 to a fake worm also on h0, mirrored on h1.0.0
(a.k.a. h2) took 73 minutes, so I got 25,648,871 bytes per minute
throughput.  I verified that the copy on h1.0.0 was correct.

Here's my configuration:

	config h0
	service    fs
	[ uninteresting ip configuration omitted ]
	filsys main cp(h0)0.25f{p(h0)25.75p(h1.0.0)25.75}
	filsys dump o
	filsys other p(h1.0.0)0.25
	ream other
	ream main
	end

{} is the mirror device, analogous to () and [].  The first device
inside {} is the master, any others are mirrors.  The code can be
found at www.collyer.net/~geoff/9/.  I'll add some commentary on the
changes later today.  They fall into several categories:

- fixes to latent bugs.
- addition of some missing switch cases for Devfworm, Devnone and Devide.
  the file server could really use a device switch (rather than a lot of
  switch statements scattered throughout the code).
  in particular, device configuration strings are now printed better.
- additional paranoia in the IDE code; specifying a non-existent drive
  no longer causes a kernel page fault.
- converted nemo's style back to the original style, and some tidying up.
- probably vestigial paranoia traceable to hunting down the fpinit bug.
- local configuration (e.g., timezone).  you'll want to crank MAXMEG up.
- addition of the mirror device.
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