Date: Wed, 2 Aug 2006 17:33:40 +1000 From: Peter Jeremy <peterjeremy@optushome.com.au> To: Tim Kientzle <kientzle@freebsd.org> Cc: freebsd-hackers@freebsd.org Subject: Re: [PATCH] adding two new options to 'cp' Message-ID: <20060802073340.GA713@turion.vk2pj.dyndns.org> In-Reply-To: <44D04797.1040201@freebsd.org> References: <44CE199C.2020500@centtech.com> <17614.8289.134373.387558@bhuda.mired.org> <96b30c400607310847s1d2f845eo212b234d03f51e9a@mail.gmail.com> <17614.10982.499561.139268@bhuda.mired.org> <ealpn1$lan$1@sea.gmane.org> <20060801072611.GA717@turion.vk2pj.dyndns.org> <20060801171150.GB3413@megan.kiwi-computer.com> <44CF8F1A.5090506@centtech.com> <20060801174048.GE3413@megan.kiwi-computer.com> <44D04797.1040201@freebsd.org>
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--BXVAT5kNtrzKuDFl Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Tue, 2006-Aug-01 23:35:03 -0700, Tim Kientzle wrote: >The "cheap" solution is to handle it purely on >extract: Detect blocks of zeros when restoring >files and seek over them. The downside is that you wind up with a sparse file whether or not you wanted one. > I simply dislike >the GNU tar approach, in part because it requires >two passes over the file (the map of holes is required >before the file is written). Actually, the only real solution to copying sparse files is to add a system call that can return a map of holes. This would neatly address the "needs two passes" problem with tar. As a general comment (not addressed to Tim): There _is_ a downside to sparsifying files. If you take a sparse file and start filling in the holes, the net result will be very badly fragmented and hence have very poor sequential I/O performance. If you're never going to update a file then making it sparse makes sense, if you will be updating it, you will get better performance by making it non-sparse. --=20 Peter Jeremy --BXVAT5kNtrzKuDFl Content-Type: application/pgp-signature Content-Disposition: inline -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.4 (FreeBSD) iD8DBQFE0FVU/opHv/APuIcRAiy3AJwNeZ3VgF2T69oKJlImDOw/bkCToACeMCXT TjXcuJ866a2PuQ6+fbSbaxE= =p4ti -----END PGP SIGNATURE----- --BXVAT5kNtrzKuDFl--
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