From owner-freebsd-questions@FreeBSD.ORG Sat Oct 17 22:30:42 2009 Return-Path: Delivered-To: freebsd-questions@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id 40FA31065670 for ; Sat, 17 Oct 2009 22:30:42 +0000 (UTC) (envelope-from vogelke@hcst.com) Received: from beta.hcst.com (beta.hcst.com [192.52.183.241]) by mx1.freebsd.org (Postfix) with ESMTP id 03FE28FC18 for ; Sat, 17 Oct 2009 22:30:41 +0000 (UTC) Received: from beta.hcst.com (localhost [127.0.0.1]) by beta.hcst.com (8.13.8/8.13.8/Debian-3) with ESMTP id n9HMUetV010610 for ; Sat, 17 Oct 2009 18:30:40 -0400 Received: (from vogelke@localhost) by beta.hcst.com (8.13.8/8.13.8/Submit) id n9HMUe8U010609; Sat, 17 Oct 2009 18:30:40 -0400 Received: by kev.msw.wpafb.af.mil (Postfix, from userid 32768) id DB832BE72; Sat, 17 Oct 2009 18:29:19 -0400 (EDT) To: freebsd-questions@freebsd.org In-reply-to: <20091016213732.GA61433@gizmo.acns.msu.edu> (message from Jerry McAllister on Fri, 16 Oct 2009 17:37:32 -0400) Organization: Oasis Systems Inc. X-Disclaimer: I don't speak for the USAF or Oasis. X-GPG-ID: 1024D/711752A0 2006-06-27 Karl Vogel X-GPG-Fingerprint: 56EB 6DBF 4224 C953 F417 CC99 4C7C 7D46 7117 52A0 Message-Id: <20091017222919.DB832BE72@kev.msw.wpafb.af.mil> Date: Sat, 17 Oct 2009 18:29:19 -0400 (EDT) From: vogelke+unix@pobox.com (Karl Vogel) Subject: Re: small question about tape-based dumps X-BeenThere: freebsd-questions@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list Reply-To: vogelke+unix@pobox.com List-Id: User questions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Sat, 17 Oct 2009 22:30:42 -0000 >> On Fri, 16 Oct 2009 17:37:32 -0400, >> Jerry McAllister said: J> You can easily put more than one dump on a tape if there is room enough J> for them. I actually rewind and skip between each dump of multiples J> made to the same tape. I also use the no-rewind device for the tape. Whenever possible, I set aside a 4-8 Gb partition for a staging area. This has helped me avoid several nasty tape problems: a. Dump to a file on the staging area, compressing it if possible. b. Get an MD5/SHA1/whatever signature for the dump. c. Write it to tape. When all the dumps are finished, rewind the tape. Read each tape file, get the signature, and compare it to what you got before; this way, you know your backup is good. Tapes stretch and wrinkle, tape heads get out of alignment, tapes can "bleed" over time, etc. There are few things worse than trying to restore someone's file and finding out you have a screwed backup. Another advantage of a staging area is better tape use; if you're copying a single file to tape (most of which is still in cache from the signature check), the tape drive won't spend as much time polishing the heads waiting for something to write. -- Karl Vogel I don't speak for the USAF or my company The RAID was dirty *and* degraded (insert "your mom" joke here). --Mike Markley on Slashdot discussing Linux drives