03-20-2013, 09:17 AM
Registered: May 2005
Location: Atlanta Georgia USA
Distribution: Redhat (RHEL), CentOS, Fedora, Debian, FreeBSD, HP-UX, Solaris, SCO
From the CentOS5 vgcreate man page:
-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 with-
out 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.
If the volume group metadata uses lvm1 format, extents can vary
in size from 8KB to 16GB and there is a limit of 65534 extents
in each logical volume. The default of 4 MB leads to a maximum
logical volume size of around 256GB.
If the volume group metadata uses lvm2 format those restrictions
do not apply, but having a large number of extents will slow
down the tools but have no impact on I/O performance to the log-
ical volume. The smallest PE is 1KB.
The 2.4 kernel has a limitation of 2TB per block device.
Interestingly that detail doesn't appear in the RHEL6 vgcreate man page any longer.