Hi guys.

What is the LVM default extent size? is it changeable? is it different between distributions?

From the man page of vgcreate:

       -s, --physicalextentsize PhysicalExtentSize[kKmMgGtT]
              Sets  the  physical  extent size on physical volumes of this volume group.  A size suffix (k for kilobytes up to t
              for terabytes) is optional, megabytes is the default if no suffix is present.  The default is 4 MB and it must  be
              at least 1 KB and a power of 2.

              Once this value has been set, it is difficult to change it without recreating the volume group which would involve
              backing up and restoring data on any logical volumes.  However, if no extents need moving for  the  new  value  to
              apply, it can be altered using vgchange -s.
...

All of that could be learned by reading the documentation. Default extent size is 4M, it's changeable, although with some caveats, and some distributions use other default values when creating a volume group in the installer.

Thank you very much.

The LVM docs haven't been fully updated from LVM1 to LVM2.

According to the official LVM howto, the default extent size is now 32M.

I can't post URLs yet, so here's a quote, search on it (in quotes) to get a confirmation:

>> You can also specify the extent size with this command if the default of 32MB is not suitable for you with the '-s' switch. In addition you can put some limits on the number of physical or logical volumes the volume can have.

Yes, one caveat to really concern yourself is the largest lv size allowable by your extent size.

And the maximum allowable pv size...