LVM: 200G + 200G = 376G ?!?

[Brian Gaynor]

On Wed, 2005-08-10 at 19:11 +0200, Colin Brace wrote:
> Hi all,
> 
> I have two 200G HDs with which I would like to create is single LVM volume.
> 
> To begin with, I created one single primary partition on each of the
> drives. Here is the fdisk output:
> 
> Disk /dev/sda: 200.0 GB, 200049647616 bytes
> 255 heads, 63 sectors/track, 24321 cylinders
> Units = cylinders of 16065 * 512 = 8225280 bytes
> 
> Device Boot      Start         End      Blocks   Id  System
> /dev/sda1               1       24321   195358401   83  Linux
> 
> Disk /dev/sdb: 203.9 GB, 203928109056 bytes
> 255 heads, 63 sectors/track, 24792 cylinders
> Units = cylinders of 16065 * 512 = 8225280 bytes
> 
> Device Boot      Start         End      Blocks   Id  System
> /dev/sdb1               1       24792   199141708+  83  Linux
> 
> Next I ran pvcreate on each. With vgcreate I then created a groups
> called "zinka" consisting of /dev/sda1 /dev/sdb1
> 
> Now I wanted to create a single logical volume called "films":
> 
>     lvcreate -n films -L 400G zinka
> 
> However, lvcreate complained:
> 
>     Insufficient free extents (96310) in volume group zinka: 102400 required
> 
> By trial and error, I discovered that I could only make a volume 376G in
> size. What is happening to those other 24Gs?

fdisk is giving you the size in decimal GB (i.e. 1GB = 1,000,000,000 or
10^9 bytes), whereas it would appear lvcreate is looking for binary GB,
which should really be called GiB, not GB (1GiB = 1,073,741,824 or 2^30
bytes).

Divide the 403.9 total GB given by fdisk by 1,073,741,824 to get GiB and
you'll get 376.16GiB.

-- 
Brian Gaynor
www.pmccorp.com
FC4/Linux on DELL Inspiron 5160 3.0Ghz 
canis 11:37:02 up 3:14, 2 users, 
load average: 0.26, 0.21, 0.18