Add devices/data_alignment_detection to lvm.conf.

Adds 'data_alignment_detection' config option to the devices section of
lvm.conf.  If your kernel provides topology information in sysfs (linux
>= 2.6.31) for the Physical Volume, the start of data area will be
aligned on a multiple of the ’minimum_io_size’ or ’optimal_io_size’
exposed in sysfs.

minimum_io_size is used if optimal_io_size is undefined (0).  If both
md_chunk_alignment and data_alignment_detection are enabled the result
of data_alignment_detection is used.

Signed-off-by: Mike Snitzer <snitzer@redhat.com>

1 files changed, 14 insertions, 2 deletions

diff --git a/man/lvm.conf.5.in b/man/lvm.conf.5.in
index 7b3ee228..6f03507b 100644
--- a/man/lvm.conf.5.in
+++ b/man/lvm.conf.5.in
@@ -137,11 +137,23 @@ has been reused without wiping the md superblocks first.
 directly upon an md device, LVM2 will align its data blocks with the
 md device's stripe-width.
 .IP
+\fBdata_alignment_detection\fP \(em If set to 1, and your kernel provides
+topology information in sysfs for the Physical Volume, the start of data
+area will be aligned on a multiple of the ’minimum_io_size’ or
+’optimal_io_size’ exposed in sysfs.  minimum_io_size is the smallest
+request the device can perform without incurring a read-modify-write
+penalty (e.g. MD's chunk size).  optimal_io_size is the device's
+preferred unit of receiving I/O (e.g. MD's stripe width).  minimum_io_size
+is used if optimal_io_size is undefined (0).  If both \fBmd_chunk_alignment\fP
+and \fBdata_alignment_detection\fP are enabled the result of
+\fBdata_alignment_detection\fP is used.
+.IP
 \fBdata_alignment\fP \(em Default alignment (in KB) of start of data area
 when creating a new Physical Volume using the \fBlvm2\fP format.
 If a Physical Volume is placed directly upon an md device and
-\fBmd_chunk_alignment\fP is enabled this parameter is ignored.
-Set to 0 to use the default alignment of 64KB or the page size, if larger.
+\fBmd_chunk_alignment\fP or \fBdata_alignment_detection\fP is enabled
+this parameter is ignored.  Set to 0 to use the default alignment of
+64KB or the page size, if larger.
 .IP
 \fBdata_alignment_offset_detection\fP \(em If set to 1, and your kernel
 provides topology information in sysfs for the Physical Volume, the