Documentation update

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
diff --git a/HOWTO b/HOWTO
index 5156adb..99cbaea 100644
--- a/HOWTO
+++ b/HOWTO
@@ -170,7 +170,7 @@
 a string. The following types are used:
 
 str	String. This is a sequence of alpha characters.
-int	Integer. A whole number value, may be negative.
+int	Integer. A whole number value, can be negative.
 siint	SI integer. A whole number value, which may contain a postfix
 	describing the base of the number. Accepted postfixes are k/m/g,
 	meaning kilo, mega, and giga. So if you want to specify 4096,
@@ -249,12 +249,12 @@
 		If set, fio will use POSIX_FADV_SEQUENTIAL for sequential
 		IO and POSIX_FADV_RANDOM for random IO.
 
-size=siint	The total size of file io for this job. This may describe
-		the size of the single file the job uses, or it may be
-		divided between the number of files in the job. If the
-		file already exists, the file size will be adjusted to this
-		size if larger than the current file size. If this parameter
-		is not given and the file exists, the file size will be used.
+size=siint	The total size of file io for this job. Fio will run until
+		this many bytes has been transferred, unless runtime is
+		limited by other options (such as 'runtime', for instance).
+		Unless specific nr_files and filesize options are given,
+		fio will divide this size between the available files
+		specified by the job.
 
 filesize=siint	Individual file sizes. May be a range, in which case fio
 		will select sizes for files at random within the given range
@@ -419,7 +419,9 @@
 		new random offset without looking at past io history. This
 		means that some blocks may not be read or written, and that
 		some blocks may be read/written more than once. This option
-		is mutually exclusive with verify= for that reason.
+		is mutually exclusive with verify= for that reason, since
+		fio doesn't track potential block rewrites which may alter
+		the calculated checksum for that block.
 
 nice=int	Run the job with the given nice value. See man nice(2).