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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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