Re: [linux-lvm] LVM Overhead

[Tomasz Chmielewski <mangoo wpkg org>]

Chris Cox schrieb:
> Joseph L. Casale wrote:
> > Hi,
> > I am wanting to use LVM behind an iet iscsi target and I am wondering
> > how much overhead if any does LVM add? Would the performance degrade
> > any, currently I am exporting full unpartitioned discs and am happy with
> > the performance. From what I am reading now, I would likely partition
> > the physical discs and use that in LVM then export a volume.
>
> Overhead is negligible.  I haven't seen any impact at all.

Quite the contrary - unless the default settings are not changed.


By default, the readahead values for LVM volumes is quite low / for 
iSCSI, I always have to change it to get acceptable performance (one 
might want to replace the $HOSTNAME with the name of the PV, or define a 
separate list; "setra" values might need some experimenting, too):


LVMS=$(/bin/ls /dev/$HOSTNAME/)

for LVM in $LVMS
    do
        blockdev --setra 16384 /dev/$HOSTNAME/$LVM
    done


--
Tomasz Chmielewski
http://blog.wpkg.org