Bug 621684

Following describes speaks about LVM; but the same applies to LUKS.

+++ This bug was initially created as a clone of Bug #621673 +++

Description of problem:
The new standard in the storage industry is to default alignment of data
areas to 1MB.  fdisk, parted, and mdadm have all been updated to this
default.

Update LVM to align the PV's data area start (pe_start) to 1MB.  This
provides a more useful default than the previous default of 64K (which
generally ended up being a 192K pe_start once the first metadata area
was created).

Having recently boasted about the new 1MB default in the RHEL6 storage
stack I was soon faced with the harsh reality that LVM was a weak link
(on legacy hardware that doesn't export I/O topology limits).

This meant that an 8 disk HW raid0 array (with 64K chunk_size) ended up
having a PV pe_start that was not aligned on a full-stripe boundary.  As
such the array was misaligned -- resulting is suboptimal performance. 
The array would've been configured optimally "out of the box" had LVM
used a default alignment of 1MB.

Steps to Reproduce:
1. pvcreate /dev/sdd
2. vgcreate test /dev/sdd
3. pvs -o name,vg_mda_size,pe_start
  
Actual results:
# pvs -o name,vg_mda_size,pe_start                                                                                                                                     
  PV         VMdaSize  1st PE
  /dev/sdd     188.00k 192.00k

Expected results:
# pvs -o name,vg_mda_size,pe_start                                                                                                                                     
  PV         VMdaSize  1st PE
  /dev/sdd    1020.00k   1.00m

--- Additional comment from msnitzer on 2010-08-05 15:27:48 EDT ---

Patch posted to lvm-devel:
http://www.redhat.com/archives/lvm-devel/2010-August/msg00035.html