Re: LVM over raid : extent size calculation
On Monday 11 December 2006 07:57, Tim Post wrote:
> My question is , what is the correct way to calculate the physical
> extent size of a volume group relative to the size of the array?
From man vgcreate:
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.
It's a tradeoff. If you use smaller extents you may not be able
to grow beyond a certain size in LVM1 and even if you convert to
LVM2 some tools (but not normal usage) may be slow. OTOH, if you
use larger extents you waste some space if you have lots of small
logical volumes.
FWIW, I have always used 32MB extents.
--Mike Bird
Reply to: