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