RE: [linux-lvm] LVM Overhead

["Joseph L. Casale" <jcasale activenetwerx com>]

Thanks guys!
You'll have to bear with me here, but how and where do I run the commands you noted here to set this value?

Thanks!
jlc

-----Original Message-----
From: linux-lvm-bounces redhat com [mailto:linux-lvm-bounces redhat com] On Behalf Of Tomasz Chmielewski
Sent: Monday, September 24, 2007 9:16 AM
To: LVM general discussion and development
Subject: Re: [linux-lvm] LVM Overhead

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

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