Re: [linux-lvm] LVM Overhead

[Chris Cox <chris_cox@stercomm.com>]

Joseph L. Casale wrote:
> 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?

I'd probably create an init script and have it executed for a given
runlevel after the mounts are done.

Some distros have a mechanism to add "user" things to end of
the init process, but if not, just grab an init script and
mod it to do the blockdev commands you need (you could make
it smart so that it does some sort of checking for valid
names, etc.)

> 
> 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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> 
> 
> 
> 
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