Partitioning FC11 ??

[Albert Graham]

On 07/20/2009 02:40 PM, Don Quixote de la Mancha wrote:
> A kernel developer, I think from Red Hat, said on a list that lvm is
> 2% slower than a physical partition.
>
> Considering the obsession some folks have with performance, that seems
> like an awful lot to give up for some flexibility which really may not
> be at all helpful to some users.
>
> The reason for the overhead is basically that when you send the
> command over the wire to the actual disk, you have to give it an
> absolute Logical Block Address - relative to the beginning of the
> whole hard drive.  Hard disk drives don't know from partitions or
> logical volumes.
>
> To convert a partition offset into a disk offset, you just add the
> starting sector of the disk.  To get that starting sector, you have to
> look it up in a data structure that's maintained by the disk driver.
>
> I don't know how LVM is implemented, but I imagine there are some
> extra layers of indirection that enable that flexibility.  The data
> structures involved will be more complex, as will be the code.
>
> They will also be more likely to be buggy as well.
>
> I've been setting up a bunch of partitions to run virtual machines on,
> for cross-platform development.  While it's a PITA to keep
> repartitioning my RAID 5, I figure the extra effort is worth it for
> that consistently 2% faster disk I/O.
>
> Don Quixote
> quixote at dulcineatech.com
> http://www.dulcineatech.com/
>
>     Dulcinea Technologies: Software of Elegance and Beauty
>
>    
Thanks Don,

I was going to make those exact points, however for performance reasons 
I go one step further and use the entire array without any partitions - 
this gives perfect raid chunk alignment :), and was infact the only way 
I could get the parallel and horizontal performance I needed (wanted).

Albert.