[linux-lvm] pvresize missing 500GB or more

[linux-lvm] pvresize missing 500GB or more

[Marc Roos]

We have a reshaped a raid5 array from 11TB to 14TB, on top of this we 
have a drbd device that resized to  14994.5 GB, 14994541563904 bytes, 
but after the pvresize I have 


pvdisplay
  --- Physical volume ---
  PV Name               /dev/drbd21
  VG Name               VGstorage21
  PV Size               13.64 TB / not usable 948.00 KB
  Allocatable           yes
  PE Size (KByte)       4096
  Total PE              3574977
  Free PE               717377
  Allocated PE          2857600


Is it normal to have this much loss?

Thanks in advance,
Marc





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Re: [linux-lvm] pvresize missing 500GB or more

[Lars Ellenberg]

On Tue, Jun 25, 2013 at 11:45:59PM +0200, Marc Roos wrote:
> 
> We have a reshaped a raid5 array from 11TB to 14TB, on top of this we 
> have a drbd device that resized to  14994.5 GB, 14994541563904 bytes, 
> but after the pvresize I have 
> 
> 
> pvdisplay
>   --- Physical volume ---
>   PV Name               /dev/drbd21
>   VG Name               VGstorage21
>   PV Size               13.64 TB / not usable 948.00 KB
>   Allocatable           yes
>   PE Size (KByte)       4096
>   Total PE              3574977
>   Free PE               717377
>   Allocated PE          2857600
> 
> 
> Is it normal to have this much loss?
> 
> Thanks in advance,
> Marc

Don't confuse SI units with "binary" units.

pvdisplay TB are actually TiB.

1000 != 1024
1000 * 1000 * 1000 * 1000 != 1024 * 1024 * 1024 * 1024

x**y --> x to the power of y

10**12 / 2**40  = 0.91
2**40 / 10**12  = 1.1

14994541563904 / 2 ** 40
13.64

So yes, in the "terra" range,
it is normal to have about 10 percent "loss"
due to "unit confusion".

more recent LVM tools try to make that clear by using
TB, GB vs TiB, GiB and so on.

you can specify --units in lower case letters for "base 1024",
upper case for "base 1000" units.

pvdisplay --units t
pvdisplay --units T

pvdisplay --units g
pvdisplay --units G

(same goes for all lvm tools)

	Lars

-- 
: Lars Ellenberg
: LINBIT | Your Way to High Availability
: DRBD/HA support and consulting http://www.linbit.com

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