Can I use LVM2 with kernel 2.6.27? Thanks everyone! On Mon, Sep 21, 2009 at 7:33 AM, Mike Snitzer <snitzer@xxxxxxxxx> wrote: > On Thu, Sep 17, 2009 at 8:37 AM, Michal Soltys <soltys@xxxxxxxx> wrote: >> Linux Raid Study wrote: >>> >>> Hello: >>> >>> Has someone experimented with LVM and Raid5 together (on say, 2.6.27)? >>> Is there any performance drop if LVM/Raid5 are combined vs Raid5 alone? >>> >>> Thanks for your inputs! >> >> Few things to consider when setting up LVM on MD raid: >> >> - readahead set on lvm device >> >> It defaults to 256 on any LVM device, while MD will set it accordingly to >> the amount of disks present in the raid. If you do tests on a filesystem, >> you may see significant differences due to that. YMMV depending on the type >> of used benchmark(s). >> >> - filesystem awareness of underlying raid >> >> For example, xfs created on top of raid, will generally get the parameters >> right (stripe unit, stripe width), but if it's xfs on lvm on raid, then it >> won't - you will have to provide them manually. >> >> - alignment between LVM chunks and MD chunks >> >> Make sure that extent area used for actual logical volumes start at the >> boundary of stripe unit - you can adjust the LVM's metadata size during >> pvcreate (by default it's 192KiB, so with non-default stripe unit it may >> cause issues, although I vaguely recall posts that current LVM is MD aware >> during initialization). Of course LVM must itself start at the boundary for >> that to make any sense (and it doesn't have to be the case - for example if >> you use partitionable MD). > > All of the above have been resolved in recent LVM2 userspace (2.02.51 > being the most recent release with all these addressed). The last > issue you mention (partitionable MD alignment offset) is also resolved > when a recent LVM2 is coupled with Linux 2.6.31 (which provides IO > Topology support). > > Mike > -- To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
