[linux-lvm] I'm confused

William Blunn bill+f.9sfuw6uo at tao-group.com
Mon Dec 9 04:16:02 UTC 2002

> > I think hardisk manufacturers use base 10, rather than base 2, when they
> > speak  of "mega" and "giga", ie. mega = 1000K and not 1024K. That means
> > that a 120G  hardisk is only 114.4G. Hence, 109.77G + about 3G = about
> > 113G. Hmm, still  about 1.5G missing.
> They also quote the size before laying down timing tracks
> and bad block mappings -- along with the bad blocks. That
> accounts for another 10%.

What you are saying is completely wrong.

When a drive manufacturer quotes a drive with a capacity of 100 GB, what
they are quoting is the *user* capacity.

There are at least 100 GB available to the "user".

The "user" is the host machine.

For a typical 512 byte block size that will mean that there will be at

   100 x 10^9 / 512 blocks

   195 312 500 blocks

available to the *user*, i.e. the host machine.

Whatever the drive uses internally is not counted.

If you look at drive specs, you will sometimes see a figure quoted for
"user data sectors" (in this case 195 312 500) and this always indicates
a capacity higher than the quoted drive capacity.

William H. Blunn - <bill+s.9sfuw6uo at tao-group.com> - Developer Support
62/63 Suttons Business Park, Earley, READING, RG6 1AZ, United Kingdom
Tel: +44 118 901 2999 - Fax: +44 118 901 2963 - http://tao-group.com/

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