[linux-lvm] LVM Overhead
Chris Cox
chris_cox at stercomm.com
Mon Sep 24 16:34:40 UTC 2007
Tomasz Chmielewski wrote:
> 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
>
>
Hmmm, perhaps for iSCSI. But using fibre SAN, I saturate my
2Gbps link (almost 200MB/sec).
--
Chris Cox
Sr. Unix Sys Admin
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