From owner-freebsd-questions@FreeBSD.ORG Mon Aug 10 16:25:31 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 401BD1065698 for ; Mon, 10 Aug 2009 16:25:31 +0000 (UTC) (envelope-from rsmith@xs4all.nl) Received: from smtp-vbr10.xs4all.nl (smtp-vbr10.xs4all.nl [194.109.24.30]) by mx1.freebsd.org (Postfix) with ESMTP id B06EC8FC21 for ; Mon, 10 Aug 2009 16:25:30 +0000 (UTC) Received: from slackbox.xs4all.nl (slackbox.xs4all.nl [213.84.242.160]) by smtp-vbr10.xs4all.nl (8.13.8/8.13.8) with ESMTP id n7AGPSOi040571; Mon, 10 Aug 2009 18:25:28 +0200 (CEST) (envelope-from rsmith@xs4all.nl) Received: by slackbox.xs4all.nl (Postfix, from userid 1001) id 9C57ABA8A; Mon, 10 Aug 2009 18:25:28 +0200 (CEST) Date: Mon, 10 Aug 2009 18:25:28 +0200 From: Roland Smith To: Jay Hall Message-ID: <20090810162528.GA49364@slackbox.xs4all.nl> References: <6206A242-7226-48E3-8D09-A1D3A651F2A8@socket.net> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="liOOAslEiF7prFVr" Content-Disposition: inline In-Reply-To: <6206A242-7226-48E3-8D09-A1D3A651F2A8@socket.net> X-GPG-Fingerprint: 1A2B 477F 9970 BA3C 2914 B7CE 1277 EFB0 C321 A725 X-GPG-Key: http://www.xs4all.nl/~rsmith/pubkey.txt X-GPG-Notice: If this message is not signed, don't assume I sent it! User-Agent: Mutt/1.5.20 (2009-06-14) X-Virus-Scanned: by XS4ALL Virus Scanner Cc: freebsd-questions@freebsd.org Subject: Re: Backup Size X-BeenThere: freebsd-questions@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: User questions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 10 Aug 2009 16:25:31 -0000 --liOOAslEiF7prFVr Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Mon, Aug 10, 2009 at 10:21:58AM -0500, Jay Hall wrote: > I am sure there is an easy explanation for this, but I cannot find it. >=20 > I am backing up my /etc directory using the following command. >=20 > tar -cvf - /etc | dd of=3D/dev/nsa1 obs=3D10240 Why are you using dd? Tar was originally built to write to tape: tar -cvf /dev/nsa1 /etc > When the command completes, I receive the following message. >=20 > 3080+0 records in > 154+0 records out > 1576960 bytes transferred in 0.179921 secs (8764740 bytes/sec) >=20 > What concerns me is when running du -h /etc, the size of the folder is = =20 > reported as 1.7M. du rounds sizes up to the filesystem block size, which is 512 bytes by default. So you'll bound to see differences. And see below. =20 > Is the number of bytes written to the tape less than the reported size = =20 > of the directory because of the way the files are written to the =20 > tape? If so, how can the amount of space used be calculated? =20 The fact that you are using tar also plays a part. Tar has some overhead to store information about the files it contains. If you want to know the total size of all files: find /etc -type f -ls | awk \ 'BEGIN {t=3D0; c=3D0}; END {print t " bytes in " c " files"}; {t=3Dt+$7; c+= +}' This returns '1320254 bytes in 362 files' in my case, while the tar/dd combo returns 1617920 bytes. The difference is the overhead for tar. If you really want to check if tar does the right thing, restore the backup= to a different place (e.g. /tmp/etc) and check with diff: # rewind your tape to the correct position (not shown) cd /tmp; tar xvf /dev/nsa1 diff -ru /etc /tmp/etc The diff command should give no output. Roland --=20 R.F.Smith http://www.xs4all.nl/~rsmith/ [plain text _non-HTML_ PGP/GnuPG encrypted/signed email much appreciated] pgp: 1A2B 477F 9970 BA3C 2914 B7CE 1277 EFB0 C321 A725 (KeyID: C321A725) --liOOAslEiF7prFVr Content-Type: application/pgp-signature Content-Disposition: inline -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.12 (FreeBSD) iEYEARECAAYFAkqASfgACgkQEnfvsMMhpyUJDACfbU+C7Sengxwhj/gStUvr4Aif zI4AnR/Lk8T+j51fhKnxWQf+kAdKjKdR =8il/ -----END PGP SIGNATURE----- --liOOAslEiF7prFVr--