On Sun, Jul 22, 2012 at 11:22:39AM -0700, Linda Walsh wrote: > > > > I was trying to figure out why I didn't get performance out of my RAID, > except when operating on really large files where it's many stripes > v. 1 stripe. > > I have 12 data disks in a RAID 50 (3 RAID5's in a RAID0) and use a suggested > stripesize of 64k, so a stripe-width of 768k. > > Some issues that have been nagging me though are getting my allocations > lined up on 768k boundaries. xfs is no prob -- tell it 64k and 12 > and it does it. > > But I just realized that lvm doesn't really tell me where it is > aligning things pvs --units s -o pv_name,vg_name,pe_start pvcreate: --metadatasize, --dataalignment, --dataalignmentoffset vgcreate: --physicalextentsize > and worse, only lets me align both chunksizes for lv's and extents for vg's > in powers of 2. Um... Not a multiple of 4k? or 64k? > > Am I wrong in thinking this would tend to give me both pv's and lv's that > are very likely NOT to be stripe-width aligned, but, worse, not stripewidth > alignable, at all. > > This would mean that a high performance file system aware of RAID > stripe with > that tries to allocate chunks starting on a 768k boundary are likely > to just > get it completely wrong? No? > > Or what am I missing? If you get the pvcreate --dataalignment right, Any PE size 256k and larger will be fine, just make sure you allocate your LV sizes in multiple of 3 PEs. lvcreate -n lv_bla -l $(( (lv_size_kb / pe_size_kb + 2) / 3 * 3 )) vg_foo -- : Lars Ellenberg : LINBIT | Your Way to High Availability : DRBD/HA support and consulting http://www.linbit.com _______________________________________________ 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/
