From owner-freebsd-questions Fri Sep 18 17:56:49 1998 Return-Path: Received: (from majordom@localhost) by hub.freebsd.org (8.8.8/8.8.8) id RAA14586 for freebsd-questions-outgoing; Fri, 18 Sep 1998 17:56:49 -0700 (PDT) (envelope-from owner-freebsd-questions@FreeBSD.ORG) Received: from post.mail.demon.net (post-20.mail.demon.net [194.217.242.27]) by hub.freebsd.org (8.8.8/8.8.8) with ESMTP id RAA14573 for ; Fri, 18 Sep 1998 17:56:41 -0700 (PDT) (envelope-from searle@longacre.demon.co.uk) Received: from [158.152.156.24] (helo=longacre.demon.co.uk) by post.mail.demon.net with smtp (Exim 2.03 #1) id 0zKBJn-0001ld-00; Sat, 19 Sep 1998 00:56:10 +0000 Date: Sat, 19 Sep 1998 01:49:04 +0100 (BST) From: Michael Searle Subject: Re: Root Disk Backup. To: freebsd-questions@FreeBSD.ORG cc: Robert Clark , "freebsd-questions@FreeBSD.ORG" In-Reply-To: <19980918124926.A1848@top.worldcontrol.com> Message-ID: MIME-Version: 1.0 Content-Type: TEXT/PLAIN; CHARSET=US-ASCII X-Organization: Who, me? X-Mailer: ANT RISCOS Marcel [ver 1.46] Sender: owner-freebsd-questions@FreeBSD.ORG Precedence: bulk X-Loop: FreeBSD.ORG On Fri 18 Sep, brian@worldcontrol.com wrote: > On 0, Robert Clark wrote: > > > If you dump a binary image of said HD, compression won't do much. Even > > if the HD is only 10% in use, the compression algorithm won't know what > > is files, and what is deleted files. > > I generally get around 50% compression with gzip on the raw size of > the disk. bzip2 is too slow because it doesn't like compressing large > areas of similar data (blank sectors). A fully used filesystem might > not have this problem. bzip2 --repetitive-fast speeds things up a lot for such large areas. Bzip2 is still very slow compared to gzip (takes me about 3 hours to bzip2 a 600MB tar backup on a Pentium, although this is with --repetitive-best), but it does have the advantage of being recoverable from errors in the compressed archive. > > > Dumping a binary image of a "washed" disk would seem to be faster. > > I find copying a disk to disk runs at about a constant rate regardless > of the data. The compression time can change. > > > Washed areas should be easier to compress. > > Yes gzip, No bzip2. > -- csubl@csv.warwick.ac.uk To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-questions" in the body of the message