From owner-freebsd-arch  Wed Mar 14 22: 6:50 2001
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Date: Wed, 14 Mar 2001 22:06:31 -0800 (PST)
From: Matt Dillon <dillon@earth.backplane.com>
Message-Id: <200103150606.f2F66Vj38988@earth.backplane.com>
To: Garance A Drosihn <drosih@rpi.edu>
Cc: "David O'Brien" <TrimYourCc@NUXI.com>,
	Brooks Davis <brooks@one-eyed-alien.net>, freebsd-arch@FreeBSD.ORG
Subject: Re: [PATCH] add a SITE MD5 command to ftpd
References: <20010314084651.A23104@ringworld.oblivion.bg>
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:If you're going to download it anyway, then there is zero point
:to doing the MD5.  The way I'm reading this option, the ONLY
:reason to do an MD5 is to try and *-AVOID-* doing a download.
:That is all I want it for, at least.

    I'm just trying to think of the situations where a user would do
    this on a regular basis, and I simply can't imagine that
    'unnecessary downloads' would account for then a few percent of
    all the downloads made from a site.   Or even 1%.

    As far as checking to see if a file has changed or not... insofar
    as any great use of ftp for synchronizing file trees the 
    modification time and file size has been used for ages and has
    proven to work extremely well.  MD5'ing isn't going to have any great
    effect on reducing bandwidth verses simply looking at the modification
    time and file size.

    I see no point in adding a command that has so little effect on the 
    site's bandwidth useage, provides no significant enhancement of 
    operations OR security, and is yet another thing for the site
    administrator to have to worry about in regards to abuse.  Your
    comment about checking to see if a file has changed is a case in point..
    someone could very easily use the feature to check whole directory
    trees for changes with insignificant impact on them, but a huge impact
    on the server if it doesn't cache the MD5's somewhere.   A single user
    MD5ing hundreds of files would have a monsterous impact on an FTP
    server.

    On FTP servers, ls -lR is often disabled due to abuse.   Many ftp
    servers still leave it disabled.  Most large ftp respositories now
    run ls -lR as a cron job and store the results in an easily
    downloadable file precisely because of the abuse that occurs when
    users run ls -lR's.

    Frankly, I see no redeeming value for a SITE MD5 command.  It would be
    a whole lot easier for a site administrator to simply generate MD5
    lists nightly and store them in files on the ftp server itself for
    users to download, just like many do for ls -lR.  And it doesn't require
    adding another command to the FTP server to make it work either.

						-Matt


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