sfdisk: add note about alignment to man page

Addresses: https://github.com/karelzak/util-linux/issues/417
Signed-off-by: Karel Zak <kzak@redhat.com>

diff --git a/disk-utils/sfdisk.8 b/disk-utils/sfdisk.8
index e8ecf48384af0c78b399fb50409e7adb143b2b49..b72bb3217dc27e344ea7a2e032c12157e23c6b0d 100644 (file)
--- a/disk-utils/sfdisk.8
+++ b/disk-utils/sfdisk.8
@@ -35,9 +35,20 @@ never been important for Linux, and this addressing concept does not make any
 sense for new devices.
 .sp
 .B sfdisk
-(since version 2.26) aligns the start and end of partitions to
-block-device I/O limits when relative sizes are specified, or when the
-default values are used.
+(since version 2.26)
+.B aligns the start and end of partitions
+to block-device I/O limits when relative sizes are specified, when the default
+values are used or when multiplicative suffixes (e.g MiB) are used for sizes.
+It is possible that partition size will be optimized (reduced or enlarged) due
+to alignment if the start offset is specified exactly in sectors and partition
+size relative or by multiplicative suffixes.
+
+The recommended way is not to specify start offsets at all and specify
+partition size in MiB, GiB (or so).  In this case sfdisk align all partitions
+to block-device I/O limits (or when I/O limits are too small then to megabyte
+boundary to keep disk layout portable).  If this default behaviour is unwanted
+then specify offsets and sizes in sectors.  In this case sfdisk entirely
+follows specified numbers without any optimization.
 .sp
 .B sfdisk
 does not create the standard system partitions for SGI and SUN disk labels like