Improve the discard documentation. Also improve discard code in

pv_manip.c to properly account for case when pe_start=0 and the first
physical extent is to be released (currently skip the first extent to
avoid discarding the PV label).

1 files changed, 8 insertions, 4 deletions

diff --git a/doc/example.conf.in b/doc/example.conf.in
index cf318553..dfc2c701 100644
--- a/doc/example.conf.in
+++ b/doc/example.conf.in
@@ -152,11 +152,15 @@ devices {
     # pv_min_size = 2048
     pv_min_size = 512
 
-    # Issue discards to an LV's underlying PV(s) when the LV is removed.
-    # Discards inform the storage that a region is no longer in use.  If set
+    # Issue discards to a logical volumes's underlying physical volume(s) when
+    # the logical volume is no longer using the physical volumes' space (e.g.
+    # lvremove, lvreduce, etc).  Discards inform the storage that a region is
+    # no longer in use.  Storage that supports discards advertise the protocol
+    # specific way discards should be issued by the kernel (TRIM, UNMAP, or
+    # WRITE SAME with UNMAP bit set).  Not all storage will support or benefit
+    # from discards but SSDs and thinly provisioned LUNs generally do.  If set
     # to 1, discards will only be issued if both the storage and kernel provide
-    # support.  Not all storage will support or benefit from discards but SSDs
-    # or thinly provisioned LUNs generally do.
+    # support.
     # 1 enables; 0 disables.
     issue_discards = 0
 }