.B llapi_layout_ost_index_get()
stores into
.I ost_index
-the index number of the Lustre OST associated with stripe number
+the index number of the Lustre OST associated with
.I stripe_number
-in layout
+in
.IR layout .
.PP
.B llapi_layout_ost_index_set()
-sets the OST index of stripe number
+sets the OST index of
.I stripe_number
-in layout
+in
.I layout
to
.IR ost_index .
This allows an application to control which OSTs will be used to
-allocate storage for a file. Setting the OST index is currently only
-supported for stripe 0.
+allocate storage for a file. Setting the starting OST index for a file
+.RI ( stripe_number =0)
+is supported with all versions of Lustre, and other stripes in the file
+will be assigned sequentially by the filesystem. Setting the OST indices
+other than stripe 0 is only supported with Lustre 2.7 and later, and will
+return an error at file creation time for 2.6 and earlier.
.PP
It is an error to call
.B llapi_layout_ost_index_get()
.I ost_index
value of
.B LLAPI_LAYOUT_DEFAULT
-means that an index will be automatically assigned by the filesystem.
+is only valid for
+.IR stripe_number =0
+and means that an OST index will be automatically assigned by the
+filesystem and will reset previously-set
+.I stripe_number
+assignments.
.SH RETURN VALUES
.LP
.B llapi_layout_ost_index_get()
.BR llapi_layout_alloc (3),
.BR llapi_layout_file_open (3),
.BR llapi_layout (7),
-.BR liblustreapi (7)
+.BR lustreapi (7)