Dale Gallagher wrote: >The primary goal here is for flexibility and I/O performance - the >hardware RAID takes care of availability/redundancy, together with >backup media. The location of the extents of a logical volume can have a great impact on its I/O performance: 1) LVM does its best to make the logical extents physically contiguous, but pvmove(8) can be used to improve this as the need arises. 2) Here's an often neglected fact: The performance of the outer cylinders of almost any hard drive (larger than a few GB) is usually about double that of the inner cylinders of the same drive. (This is due to the fact that there are about twice as many sectors per track on the outside of the platter as there are on the inside of the platter and thus data moves past the read/write heads about twice as fast on the outer cylinders as the inner cylinders.) Therefore, to improve I/O performance, try to create often used logical volumes first as LVM tends to allocate lower physical extents first. Otherwise, use pvmove(8) to move the more frequently accessed extents to the fastest (lowest) physical extents of the fastest LVM physical volume. It is best to use (almost) whole disks as LVM physical volumes, since smaller physical volumes (partitions) would be either fast, average, or slow and not the full spectrum of fast through slow. The least accessed logical extents should be moved to the highest numbered (slow) physical extents of the slowest disks. 3) LVM striping can also be used to improve I/O performance over two or more spindles (disks). Avoid LVM striping over two physical volumes on the same spindle (disk), since this reduces performance as the system waits for seeks between these two physical volumes (for a simple sequential access). Sincerely, Ken Fuchs <kfuchs@winternet.com> _______________________________________________ linux-lvm mailing list linux-lvm@sistina.com http://lists.sistina.com/mailman/listinfo/linux-lvm read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/
