Path: utzoo!dptcdc!jarvis.csri.toronto.edu!mailrus!ames!sgi!vjs@rhyolite.SGI.COM
From: vjs@rhyolite.SGI.COM (Vernon Schryver)
Newsgroups: comp.sys.sgi
Subject: Re: backup through the fs
Summary: Look, ma! No holes.
Message-ID: <30813@sgi.SGI.COM>
Date: 17 Apr 89 21:33:20 GMT
References: <8904171554.AA19754@adt.uucp>
Sender: daemon@sgi.SGI.COM
Organization: Silicon Graphics, Inc., Mountain View, CA
Lines: 21

In article <8904171554.AA19754@adt.uucp>, madd@adt.UUCP (jim frost) writes:
>  ... [about how to handle holes] ...
> jim frost
> madd@bu-it.bu.edu

There are no holes in EFS.  Some consider that a feature, since you get
more consistency (think of cp and dd in addition to tar/cpio/bru).  Most
of us consider that an oversight which no one has had time to fix.  Holes
in an Extent FS are messier than in a fixed or semi-fixed size block FS
like FFS or BFS.  What do you do when someone writes 1 byte in the middle
of a hole?  How big an extent do you allocate?  If you allocate the largest
possible, you are almost always wrong, and waste lots of blocks.  If you
don't, and the user eventually writes nearby, then you have unnecessarily
fragemented the file.

This absense of holes in EFS may affect the utility (but not the possibility)
of omniscient backup tools.  Me?--I use tar & cpio.

Vernon Schryver
Silicon Graphics
vjs@sgi.com