Chris Cox wrote: > 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). > > I check my local drives, they all use the default 1024.... Is setting the read ahead that big of a deal with just LVM? I would think if it's an issue, it's an issue everywhere. -- Chris Cox Sr. Unix Sys Admin _______________________________________________ linux-lvm mailing list linux-lvm@redhat.com https://www.redhat.com/mailman/listinfo/linux-lvm read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/
