[linux-lvm] Query on PE size

[linux-lvm] Query on PE size

[Kumar amit mehta]

Hi,

I see that a VG will set the default PE size to 4MiB, i.e.
4 * 1024 * 1024 = 4194304 
(Please correct me if I'm wrong)

<snip>
# pvcreate /dev/vdc1
# vgcreate testvg /dev/vdc1
# vgdisplay
# vgdisplay testvg|grep "PE Size"
   PE Size               4.00 MiB <----
<snip>

I see that :
vgcreate() 
 -->vgcreate_params_set_defaults()
   -->vp_def->extent_size = DEFAULT_EXTENT_SIZE * 2;

Where DEFAULT_EXTENT_SIZE is #defined to 4096
<snip from lib/config/defaults.h>
#define DEFAULT_EXTENT_SIZE 4096        /* In KB */
<snip from lib/config/defaults.h>

This means that the default extent size being set is 8192, but as mentioned 
earlier,the default extent size as reported by 'vgdisplay' is 4 MiB. So Can
someone please point me to the place where this conversion of 8192 into 4MiB
is taking place in the code ?

-Amit

Re: [linux-lvm] Query on PE size

[Zdenek Kabelac]

Dne 5.6.2013 04:07, Kumar amit mehta napsal(a):
> Hi,
>
> I see that a VG will set the default PE size to 4MiB, i.e.
> 4 * 1024 * 1024 = 4194304
> (Please correct me if I'm wrong)
>
> <snip>
> # pvcreate /dev/vdc1
> # vgcreate testvg /dev/vdc1
> # vgdisplay
> # vgdisplay testvg|grep "PE Size"
>     PE Size               4.00 MiB <----
> <snip>
>
> I see that :
> vgcreate()
>   -->vgcreate_params_set_defaults()
>     -->vp_def->extent_size = DEFAULT_EXTENT_SIZE * 2;
>
> Where DEFAULT_EXTENT_SIZE is #defined to 4096
> <snip from lib/config/defaults.h>
> #define DEFAULT_EXTENT_SIZE 4096        /* In KB */
> <snip from lib/config/defaults.h>
>
> This means that the default extent size being set is 8192, but as mentioned
> earlier,the default extent size as reported by 'vgdisplay' is 4 MiB. So Can
> someone please point me to the place where this conversion of 8192 into 4MiB
> is taking place in the code ?

Variables in the lvm source code which have suffix _size should keep the size 
in 512b block units ->  8192 * 512b block => 4MiB

Zdenek