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From: Harti Brandt <harti@freebsd.org>
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cc: Garrett Wollman <wollman@khavrinen.lcs.mit.edu>
Subject: Re: NEW TAR
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On Wed, 21 Jul 2004, Daniel Lang wrote:

DL>To Harti:
DL>I admit I don't know for sure, but to my understanding the handling
DL>of the sparse file is done in the filesystem layer and not in the 
DL>application, right? Then all possible performance benefit on reading
DL>a sparse file should be gained anyway. Regardless if the application
DL>(the archiver) knows about the locations of the gaps or not....

I know of at least one application that does sparse file handling in the 
sense that it tries to create sparse file when the underlying FS supports
it - that is my PDP11 emulator. I have even a special zcp utility that 
may re-sparse a file by copying it and looking for 0 blocks. It's not that 
p11 depends on the file system supporting sparse files - it just tries to 
use them if they are available.

Again, for tar it's a matter of speed. Didn't Tim say that with the 
current sparse file info layout (gtar) he needs more than one pass over 
the file?

harti