Expand on fill_device option since it apparently causes confusion

[fio.git] / HOWTO

diff --git a/HOWTO b/HOWTO
index e54382b19b5e35beaa907b1cb263081d5c8bab44..e8fbd97f6ab2693920b93101e654873005516f3a 100644 (file)
--- a/HOWTO
+++ b/HOWTO
@@ -378,7 +378,11 @@ filesize=int       Individual file sizes. May be a range, in which case fio
 fill_device=bool Sets size to something really large and waits for ENOSPC (no
                space left on device) as the terminating condition. Only makes
                 sense with sequential write. For a read workload, the mount
-               point will be filled first then IO started on the result.
+               point will be filled first then IO started on the result. This
+               option doesn't make sense if operating on a raw device node,
+               since the size of that is already known by the file system.
+               Additionally, writing beyond end-of-device will not return
+               ENOSPC there.
 
 blocksize=int
 bs=int         The block size used for the io units. Defaults to 4k. Values
@@ -926,6 +930,11 @@ verify_fatal=bool  Normally fio will keep checking the entire contents
                option is set, fio will exit the job on the first observed
                failure.
 
+verify_dump=bool       If set, dump the contents of both the original data
+               block and the data block we read off disk to files. This
+               allows later analysis to inspect just what kind of data
+               corruption occurred. On by default.
+
 verify_async=int       Fio will normally verify IO inline from the submitting
                thread. This option takes an integer describing how many
                async offload threads to create for IO verification instead,
@@ -993,7 +1002,8 @@ zoneskip=int       Skip the specified number of bytes when zonesize data has
                io on zones of a file.
 
 write_iolog=str        Write the issued io patterns to the specified file. See
-               read_iolog.
+               read_iolog.  Specify a separate file for each job, otherwise
+               the iologs will be interspersed and the file may be corrupt.
 
 read_iolog=str Open an iolog with the specified file name and replay the
                io patterns it contains. This can be used to store a