Date: Mon, 10 Aug 2009 11:25:52 -0500 From: Dan Nelson <dnelson@allantgroup.com> To: Jay Hall <jhall@socket.net> Cc: freebsd-questions@freebsd.org Subject: Re: Backup Size Message-ID: <20090810162552.GD54485@dan.emsphone.com> In-Reply-To: <6206A242-7226-48E3-8D09-A1D3A651F2A8@socket.net> References: <6206A242-7226-48E3-8D09-A1D3A651F2A8@socket.net>
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In the last episode (Aug 10), Jay Hall said: > I am sure there is an easy explanation for this, but I cannot find it. > > I am backing up my /etc directory using the following command. > > tar -cvf - /etc | dd of=/dev/nsa1 obs=10240 > > When the command completes, I receive the following message. > > 3080+0 records in > 154+0 records out > 1576960 bytes transferred in 0.179921 secs (8764740 bytes/sec) > > What concerns me is when running du -h /etc, the size of the folder is > reported as 1.7M. > > Is the number of bytes written to the tape less than the reported size of > the directory because of the way the files are written to the tape? If > so, how can the amount of space used be calculated? du prints the number of disk blocks used by a directory tree. Your filesystem probably was formatted with 16k blocks and 2k fragment size; This means that the minimum space du will report for each file is 2k. Tar uses 512-byte blocks internally, so a directory with a lot of small files in it (/etc for example) will take up less space as a tar file than on disk. Try running "du -ha /etc", to see what du reports for each file under /etc. -- Dan Nelson dnelson@allantgroup.com
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