[Fedora-livecd-list] local hard disk space?

[Douglas McClendon]

Coco Computers & Consulting wrote:
> When I boot with Centos 5.1 Live CD, a df command shows the root 
> filesystem / is mounted to /dev/mapper/livecd-rw and shows a total of 
> about 4GB with 50% available. Is this disk space from my local hard 
> drive? How is it carved out? My local hard drive is installed with a 
> Windows XP system. Does LiveCD simply create a 4GB file on the local 
> hard drive for its own use?

No, the 4G is basically imaginary.  Whatever amount it starts out as
used, say 2.1G, is actually compressed data on the cdrom, i.e. about
675MB.  Once booted and files/blocks are written, they are written to
ram (or with liveusb persistence, flash/disk).  The only reason for the
arbitrary 4G number, as opposed to say, 1000G, is that the formatting
data of a larger filesystem would take up a little bit of extra space,
even compressed.  Theoretically if you had a 16GB ram system, you'd be a
bit unhappy that an artificial limitation of 4GB of writable blocks is
being used, when you have more ram than that to burn.  Long ago I
submitted a patch such that the devicemapper device would have
a size greater than 4GB, but the filesystem still be formatted to 4GB.
With that kind of patch, such a user of a 16GB filesystem could
resize2fs the filesystem larger post boot, and not be limited.  At the
time however, squashfs was not as efficient as it currently is with
sparse files, and such a larger device would also have resulted in more
actual data space taken up on the cdrom (and also signifigantly
increasing the time to author/master the livecd originally).  Now
however squashfs natively handles sparse files, and won't waste any
actual space on even a terabyte of zeros.

That was probably a longer answer than you were looking for.  Executive
summary- the 4G is purely imaginary and means nothing.  The fedora
livecd like most livecds, by default, does not touch your system disk at
all.

-dmc



> 
> --thanks,
> --Tony C.
> 
> Coco Computers & Consulting
> http://coconets.homeip.net
> 
> 
> 
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