From mboxrd@z Thu Jan  1 00:00:00 1970
Message-ID: <7948f2936ad22d2c4d5075710e8e9c49@quanstro.net>
From: erik quanstrom <quanstro@quanstro.net>
Date: Thu, 12 Feb 2009 11:52:53 -0500
To: 9fans@9fans.net
In-Reply-To: <20090212164247.GV22259@masters6.cs.jhu.edu>
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Subject: Re: [9fans] source browsing via http is back
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> On Thu, Feb 12, 2009 at 07:49:58AM -0500, erik quanstrom wrote:
> > exactly.  the point i was trying to make, and evidently
> > was being too coy about, is that 330 odd gb wouldn't
> > be as useful a number as the sum of the sizes of all the
> > new/changed files from all the dump days.  this would
> > be a useful comparison because this would give a
> > measure of how much space is saved with venti over
> > the straightforward algorithm of copying the changed
> > blocks, as ken's fileserver does.
>
> Unless I misunderstand how replica works, the 330 odd GB number [1] is
> useful as the amount of data that would have to be transfered over the wire
> to initialize a mirror.  (Since, as I understand it, a replica log of
> sourcesdump would have nothing but "add" commands for each $year/$dump/$file
> entry, and would therefore necessitate transfering each file separately).

actually not, see http://www.quanstro.net/plan9/history.pdf
i have done the process of replicating history on 4 different
fileservers.  only the *differences* need to be transfered.

> On the first hand again, given the occasional reports of "replica hosed me"
> I'm not terribly keen on trusting it and seem to recall that some of the
> fixes have involved hand-editing the replica logs on sources.  This makes me
> suspicious that some of the replica logs frozen in sourcesdump would be
> incorrect and lead to incorrect data on mirrors if used as part of the
> scheme.

i've posted a number of fixes for specific failure modes reported.
i've done about 10k replicas with my changes without any failures.
try it.  the only way to fix things is to keep working on them.

- erik