Date: Sat, 19 Sep 1998 01:49:04 +0100 (BST) From: Michael Searle <searle@longacre.demon.co.uk> To: freebsd-questions@FreeBSD.ORG Cc: Robert Clark <Clark@open.org>, "freebsd-questions@FreeBSD.ORG" <freebsd-questions@FreeBSD.ORG> Subject: Re: Root Disk Backup. Message-ID: <Marcel-1.46-0919004904-0b0cjo5@longacre.demon.co.uk> In-Reply-To: <19980918124926.A1848@top.worldcontrol.com>
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On Fri 18 Sep, brian@worldcontrol.com wrote: > On 0, Robert Clark <Clark@open.org> wrote: <snip> > > > 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
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