On Fri, Mar 19 2010 at 5:27pm -0400, Phillip Susi <psusi@cfl.rr.com> wrote: > On 3/19/2010 3:25 PM, Mike Snitzer wrote: > > Any reason why you'd like to use DOS partitioning (first primary > > partition starting at 63rd sector)? > > Convention. I am looking into using GPT instead though. > > > Anyway, if you have a recent kernel (e.g. 2.6.33) you'll be in good > > shape regardless. If you create a partition on the device (using DOS > > partitions) the kernel _should_ be aware of where the partition starts > > and tell you how far you'd have to shift the start of your LVM2 PV data > > area to get it perfectly aligned relative to the underlying physical > > block size. Check for example: > > # cat /sys/block/sda/sda1/alignment_offset > > > > But if your device is using 512b physical_sector_size you'll just have a > > 0 for alignment_offset. Check physical_block_size with: > > # cat /sys/block/sda/queue/physical_block_size > > 0 alignment, physical block size 512. > > > Also verify that your SSD device is naturally aligned (aka > > alignment_offset=0); I'd wager it is naturally aligned: > > # cat /sys/block/sda/alignment_offset > > Kernel thinks so, and based on performance tests it appears so. > > > All said, even if you have an older kernel, to manually get what you > > want (shift start to account for DOS partition at 63rd sector, align PV > > pe_start on a 512K boundary), please try: > > # pvcreate --dataalignmentoffset 512b --dataalignment 512K ... > > Won't that just add one sector to the start, placing it at sector 1025? > How does an alignment offset of 1 sector account for the partition > starting on sector 63? The --dataalignmentoffset acts as padding. I was focused on getting you to a power of 2 start (sector 64). Then from there --dataalignment governs the start boundary for the PV data area. So you're right, 64*512b + 512K isn't a multiple of 512K :) This will get you what you want: # pvcreate --dataalignmentoffset 512b --dataalignment 480K /dev/sda1 # pvs --units s -o+pe_start /dev/sda1 PV VG Fmt Attr PSize PFree 1st PE /dev/sda1 lvm2 a- 20971457S 20971457S 961S 961*512b + 63*512b = 512K _______________________________________________ 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/
