Document the verify behaviour wrt read and write workloads

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
diff --git a/HOWTO b/HOWTO
index eb8f453..aa10dbc 100644
--- a/HOWTO
+++ b/HOWTO
@@ -823,7 +823,11 @@
 
 		This option can be used for repeated burn-in tests of a
 		system to make sure that the written data is also
-		correctly read back.
+		correctly read back. If the data direction given is
+		a read or random read, fio will assume that it should
+		verify a previously written file. If the data direction
+		includes any form of write, the verify will be of the
+		newly written data.
 
 verifysort=bool	If set, fio will sort written verify blocks when it deems
 		it faster to read them back in a sorted manner. This is
diff --git a/fio.1 b/fio.1
index 9b1e02b..10b1768 100644
--- a/fio.1
+++ b/fio.1
@@ -571,7 +571,7 @@
 .RS
 .RS
 .TP
-.B md5 crc16 crc32 crc64 crc7 sha256 sha512
+.B md5 crc16 crc32 crc32c crc32c-intel crc64 crc7 sha256 sha512 sha1
 Store appropriate checksum in the header of each block.
 .TP
 .B meta
@@ -586,6 +586,12 @@
 .B null
 Pretend to verify.  Used for testing internals.
 .RE
+
+This option can be used for repeated burn-in tests of a system to make sure
+that the written data is also correctly read back. If the data direction given
+is a read or random read, fio will assume that it should verify a previously
+written file. If the data direction includes any form of write, the verify will
+be of the newly written data.
 .RE
 .TP
 .BI verify_sort \fR=\fPbool