[linux-lvm] disk capacity discrepancy: is it 1000 versus 1024?

[Greg Freemyer]

On 5/14/05, Greg Freemyer wrote:
> On 5/14/05, Maurice Volaski wrote:
> > I originally had a hardware RAID with fourteen 400 GB drives of
> > usable capacity (Hitachi 7K400) . That's 5600 GB altogether. That's
> > what both fdisk and df report (filesystem was ext3).
> >
> > When I instead created an LVM2 physical volume on the device, I get
> > just 5.09 TB.
> >
> > Is LVM eating several hundreds gigabytes of space or is it the case
> > that LVM uses terminology in a strict multiply by 1024 fashion versus
> > everything else, which is multiplying by 1000. In that case, I guess
> > the drives aren't really 400 GBs. :-(
> >
> > However, it appears that parameters passed to LVM commands are
> > interpreted using x1000, not x1024.
> >
> > other keywords: gigabinarybytes, gibibytes, Gi, terabinarybytes, tebibytes, Ti.
> > --
> >
> > Maurice Volaski, mvolaski at aecom.yu.edu
> > Computing Support, Rose F. Kennedy Center
> > Albert Einstein College of Medicine of Yeshiva University
> 
> As Maurice implies NIST is making an effort (however small) to
> standardize GB as 1000 * 1000 * 1000 bytes.
> 
> See http://physics.nist.gov/cuu/Units/binary.html
> 
> So per NIST:
> GB = Gigabyte = 1,000 * 1,000 * 1,000 Bytes
> GiB = Gibibyte  = 1,024 * 1,024 * 1,024 Bytes
> 
> Or for Maurice TB vs. TiB
> 
> BTW, the difference between TB and TiB is almost 10% so this has a
> very user observable effect and would explain Maurice's discrepancy.
> 
> So if I understand Maurice's question, it becomes:
>    "Is LVM reporting TiB units with a TB designation?"
> 
> Greg
> --
> Greg Freemyer
> The Norcross Group
> Forensics for the 21st Century
> 
Maurice,

I forgot to add that disk drive manufactures have been selling disks
by the GB for years, not the GiB.  Thus your 400 GB disk drive is most
likely about 373 GiB.  (I used a calculator).

One way to tell for sure is to get the number of sectors and multiply
it out.  Sectors are typically 512 bytes.  You can typically see the
sector count or the paper label of newer drives, or with standard ide
disks in /proc/ide/hdx/capacity.

Greg

-- 
Greg Freemyer
The Norcross Group
Forensics for the 21st Century