Introduction:

The Flexible Filesystem Benchmark (FFSB) is a filesystem performance
measurement tool.  It is a multi-threaded application (using
pthreads), written entirely in C with cross-platform portability in
mind.  It differs from other filesystem benchmarks in that the user
may supply a profile to create custom workloads, while most other
filesystem benchmarks use a fixed set of workloads.

As of version 5.1, it supports seven different basic operations, support
for multiple groups of threads with different operation mixtures,
support for operation across multiple filesystems, and support for
filesystem aging prior to benchmarking.


Differences from version 4.0 and older:

Version 5.0 and above represent almost a total re-write and many
things have changed.  In version 5.0 and above FFSB moved to a
time-regulated run versus doing a set number of different operations
and timing the whole thing.  This is primarily to better deal with the
use of multiple threadgroups which would otherwise not be synchronized
at termination time.

Additionally, the FFSB configuration file format has changed in
version 5.0, although we do support old-style configuration files
along with a run-time passed on the command line.  In this mode,
version 5.0 and above ignores the iterations parameter, and simply
uses the time specified on the command line.

Behaviorally, most of the old operations are the same -- sequential
reads and sequential writes work as they did before.  One change in
version 5.0 is the skip-read behavior of reading then seeking forward
a fixed amount then reading again is removed, we now support fully
randomized reads and writes from random offsets within the file.

Version 4.0 didn't support overwrites (only appends) so we interpret
writes in old config files to be append operations.

On Linux, CPU utilization information will only be accurate for
systems using NPTL, older Linuxthreads systems will probably only see
zeros for CPU utilization because Linuxthreads is non-compliant to
POSIX. Version 4.0 and older could be recompiled to work on
Linuxthreads, but in 5.0 and later we no longer support this.

We no longer support the "outputfile" on the command line.

One should simply use tee or similar to capture the output.  FFSB
unbuffers standard out for this purpose, and errors are sent on
standard error.

Global options:

There are eight valid global options placed at the beginning of the
profile.  Three of them are required: num_filesystems (number of
filesystems), num_threadgroups (number of threadgroups), and time
(running time of the benchmark).  The other five options are:

directio   - each call to open will be made using O_DIRECT
alignio    - aligns all block operations for random reads and writes
             on 4k boundaries.
bufferedio - currently ignored: it is intended to use libc
             fread,rwrite, instead of just unix read and write calls
verbose    - currently ignored

callout    - calls and external command and waits for its termination
	     before FFSB begins the benchmark phase.
	     This is useful for synchronizing distributed clients,
	     starting profilers, etc.

They must be specified in the above order (num_filesystems,
num_threadgroups, time, directio, alignio, bufferedio, verbose,
callout).



Filesystems:

Filesystems are specified to FFSB in the form of a directory.  FFSB
assumes that the filesystem is mounted at this directory and will not
do any verification of this fact beyond ensuring it can read/write to
the location.  So be careful to ensure something with enough space to
handle the dataset is in fact mounted at the specified location.

In the filesystem clause of the profile, one may set the starting
number of files and directories as well as a minimum and maximum
filesize for the filesystem.  One may also specify the blocksize
used for creating the files separately in the filesystem clause.

Also, if a filesystem is to be aged, a special threadgroup clause may
be embedded in a filesystem clause to specify the operation mixture
and number of threads used to age the filesystem.  This threadgroup is
run until filesystem utilization reaches the specified amount.

Inheritance --  if you are using multiple filesystems, all attributes
except the location should be inherited from the previous filesystem.
This is done to make it easier to add groups of similar filesystems.
In this case, only the location is required in the filesystem clause.

As of version 5.1, filesystem re-use is supported if a given
filesystem hasn't been modified beyond it's orginal specifications
(number of files and directories is correct, and file sizes are within
specifications).  This can be a huge time saver if one wishes to do
multiple runs on the same data-set without altering it during a run,
because the fileset doesn't need to be recreated before each run.

To do this, specify "reuse=1" in the filesystem clause, and FFSB will
verify the fileset first, and if it checks out it will use it.
Otherwise, it will remove everything and re-create the filesets for
that filesystem.

Threadgroups:

An arbitrary number of threadgroups with differing numbers of threads
and operation mixes can be specified.  The operations are specified
using a weighting for each operation, if an operation isn't specified
it's weighting is assumed to be zero (not used).

"Think-time" for a threadgroup may also be specified in millisecond
amounts using the "op_delay" parameter, where every thread will wait
for the specified amount between each operation.

Operations:

All operations begin by randomly selecting a filesystem from the list
of filesystems specified in the profile.  The distribution aims to be
uniform across all filesystems.


The seven operations are:

reads  - read() calls with an overall amount and a blocksize
         operates on existing files.  Care must be taken to ensure
         that the read amount is smaller than the size of any possible
         file.

	 If random_read is specified, then the each individual blocks
         will be read starting from a random point with the file, and
         this will continue until the entire amount specified has been
         read.  This offset of each random block will be totally
         random to the byte level, unless the "alignio" global parameter
         is on, and then the reads will be 4096 byte aligned.  This is
         generally recommended.


readall - Very similar to read above, except it doesn't take an
          amount; it simply reads the entire file sequentially using the
          read_blocksize.   This is useful for situations where
	  different filesystems have differently sized files, and sequential
	  read patterns across all filesystems are desired.

writes - write() calls with an overall amount and blocksize
         this is an overwrite operation and will not enlarge an existing
         file, again one must be careful not to specify a write amount
         that is larger than any possible file in the data set.

	 If random_write is specified, then the each individual blocks
         will be written starting from a random point with the file, and
         this will continue until the entire amount specified has been
         written out.  This offset of each random block will be totally
         random to the byte level, unless the "alignio" global parameter
         is on, and then the writes will be 4096 byte aligned.  This
         is generally recommended.

	 If the fsync_flag parameter for the threadgroup is non-zero,
	 then after all of the write calls are finished, fsync() will
	 be called on the file descriptor before the file is closed.


creates - creates a file using open() call and determines the size
          randomly between on the constraints (min_filesize and
          max_filesize) for the selected filesystem. Write operations will
          be done using the same blocksize as is specified for the
          write operation.
deletes - calls unlink() on a filename and removes it from the
          internal data-structures.  One must be careful to ensure
          there are enough files to delete at all times or else the benchmark
          will terminate.
appends - calls write() using the append flag with an overall amount
          and a blocksize to be appended onto a randomly chosen file.
metas   - this is actually a mix of several different directory
          operations.  Each "meta" operation consists of two directory
          creates, one directory remove, and a directory rename.
          These operations are all carried out separately from the
          other 5 operations.

Operation accounting:

Each operation which uses a blocksize counts each read/write of a
blocksize as an operation (reads,writes,creates, and appends) whereas
deletes and metas are considered single operations.

Running the benchmark:

There are three phases to running the benchmark, aging, fileset
creates, and the benchmark phase.

The create phase is carried out across all filesystems simultaneously
with one dedicated thread per filesystem.

After the create phase, sync() is called to ensure all dirty data gets
written out before the benchmark phase begins, and sync() is again
called at the end of the benchmark phase.  The time in sync() at the
end of the benchmark phase is counted as part of the benchmark phase.

Caveats/Holes/Bugs:

Aging and aging across multiple filesystems simultaneously hasn't been tested
very much.

If *any* i/o operation or system call/libc call fails, the benchmark
will terminate immediately.

The parser doesn't handle mal-formed or incorrect profiles very well
(or at all).

The parser doesn't check to make sure all of the appropriate options
have been specified.  For example, if writes are specified in a
threadgroup but write_blocksize isn't specified, the parse won't catch
it, but the benchmark run will fail later on.


Configuration Files (new style):

New Style Configuration allows for arbitrary newlines between lines,
and comments using '#' at the start of a line.  Also it allows tabs,
whitespace before and after configuration parameters.

The new style configuration file is broken up into three main parts:

global parameters, filesystems, and threadgroups

The sections must be in the above order.

Global parameters:

Global parameters are described above, the first three are always
required. Example:

----------

num_filesystems=1
num_threadgroups=1
time=30 		# time is in seconds

directio=0 		# don't use direct io
alignio=1  		# align random IOs to 4k
bufferedio=0		# this does nothing right now
verbose=0		# this does nothing right now

			# calls and external command and waits
			# everything until the newline is taken
			# so you can have abritrary parmeters
callout=synchronize.sh myhostname

---------

All of these must appear in this order, though you can leave out the
optional ones.

Filesystems:

Filesystems describe different logical sets of files residing in
different directorys.  There is no strict requirement that they
actually be on different filesystems, only that the directory
specified already exists.

Filesystems are specified by a clause with a filesystem number like
this:

[filesystem0]
	location=/mnt/testing/
	num_files=10
	num_dirs=1
	max_filesize=4096
	min_filesize=4096
[end0]


The clause must always begin with [filesystemX] and end with [endX]
where X is the number of that filesystem.

You should start wiht X = 0, and increment by one for each following
filesystem.  If they are out of order, things will likely break.

The required information for each filesystem is: location, num_files,
num_dirs, max_filesize, and min_filesize.  Beyond those the following
four options are supported:



reuse=1 # check the filesystem to see if it is reusable

	# filesystem aging, three components required
	# takes agefs=1 to turn it on
	# then a valid threadgroup specification
	# then a desired utilization percentage

agefs=1 # age the filesystem according to the following threadgroup
	[threadgroup0]
		num_threads=10
		write_size=40960
		write_blocksize=4096
		create_weight=10
		append_weight=10
		delete_weight=1
	[end0]
desired_util=0.20	# In this case, age until the fs is 20% full

create_blocksize=4096   # specify the blocksize to write()
		        # for creating the fileset, defaults to 4096

age_blocksize=4096      # specify the blocksize to write() for aging


Also, to allow lazy people to use lots of filesystems, we support
filesystem inheritance, which simply copies all options but the
location from the previous filesystem clause if nothing is specified.
Obviously, this doesn't work for filesystem0. (May not work for aging
either?)

Full blown filesystem clause example:

----

[filesystem0]

	# required parts

	location=/home/sonny/tmp
	num_files=100
	num_dirs=100
	max_filesize=65536
	min_filesize=4096

	# aging part
	agefs=0
	[threadgroup0]
		num_threads=10
		write_size=40960
		write_blocksize=4096
		create_weight=10
		append_weight=10
		delete_weight=1
	[end0]
		desired_util=0.02	# age until 2% full

	# other optional commands

	create_blocksize=1024		# use a small create blocksize
	age_blocksize=1024		# and smaller age create blocksize
	reuse=0	                        # don't reuse it
[end0]



--

Threadgroups:

Threadgropus are very similar to filesystems in that any number of
them can be specified in clauses, and they must be in order starting
with threadgroup0.

Example:

---

[threadgroup0]
	num_threads=32
	read_weight=4
	append_weight=1

	write_size=4096
	write_blocksize=4096

	read_size=4096
	read_blocksize=4096
[end0]

---

In a threadgroup clause, num_threads is required and must be at least
1.  Then, at least one operation must be given a weight greater than 0
to be a valid threadgroup.  Operations can be given a weighting of 0,
and in this case they are ignored.

Certain operations will also require other commands, for example, if
read_weight is greater than zero, then one must also include a
read_size and a read_blocksize.  Here's the table of requirements and
options:


Operation		Requirements			Options
--			--				--
read_weight		read_size, read_blocksize	read_random
readall_weight		read_blocksize			none
write_weight		write_size, write_blocksize	write_random,fsync_file
create_weight		write_blocksize or create_blocksize	none
append_weight		write_blocksize, write_size	none
delete_weight		none				none
meta_weight		none				none



Other threadgroup options:

op_delay=10  # specify a wait between operations in milli-seconds

bindfs=3     # This allows you to restrict a threadgroup's operation
             # to a specific filesystem number.  Currently only
	     # binding to one specific filesystem is supported