From: muhammad@chaos.utexas.edu (Muhammad Pervez)
Newsgroups: comp.unix.sysv386
Subject: ISC 3.0: Why Very Fast File System is slower?
Date: 27 Jul 92 22:15:01 GMT
Reply-To: muhammad@chaos.utexas.edu (Muhammad Pervez)
Organization: University of Texas at Austin, Center for Nonlinear Dynamics


Hi there!

  System:     486/33 EISA  running Interactive Unix V 3.2 version 3.0
  Hard disk:  Seagate, about 1400Mb, (~11ms seek time, 3-5Mb/sec transfer rate)
  Disk controller:  Adaptec aha-1740  Intelligent Host Bus Adapter (SCSI)

	I just installed ISC V 3.2 version 3.0 on my 486/33 EISA with
a 1400Mb hard disk.  I was very interested in benchmarking the 'Very
Fast File System' that ISC has introduced.  It looks to me that they
should call this 'Even Slower File System' ;-)

	From the tests I have done with the VFFS (Very Fast File System),
I am getting a performance of about half as compared to the default
file system (S51K).  Am I missing something?  I will like to hear
comments about this new file system.

   Here is what I did:

   First, I created the VFFS on /dev/dsk/c0t0s4 partition. (/usr2)

   # /etc/vf/mkvffs /dev/dsk/c0t0s4 1617920 64000 10240 10240 usr2 usr2

  where 1617920 is the size of our /usr2 partition which I got from
  /etc/partitions.

  64000 is the no. of inodes.

  10240 is the size of the primary and the secondary extent in 1K bytes.
  (Therefore 10240 corresponds to an extent size of 10Mb.)

  
	After creating the file system, I mounted it:

	# mount -f VF /dev/dsk/c0t0s4 /usr2

	Now, to benchmark it, I created a 30Mb file, named 'foo'. 
	Then used the copy command:

	# time cp foo bar
  
	I did the same thing for the default file system also.

	
	On the Very Fast File System, the above copy command took
	from 80 to 90 seconds, while on the default file system (S51K),
	it took only about 47 seconds.	

	Now I am puzzled that why the VFFS seems to be less efficient
	than the standard file system.  ISC claims that it is supposed
	to be MUCH faster than the S51K file system in transfering
	large files.

	ISC also claims that with VFFS, the transfer rate can approach
	the transfer rate of the hard disk itself.  Our hard disk's 
	lower limit on sustained transfer rate is 3Mb/sec.  With S51K, we
	can go upto 1.3Mb/sec but with VFFS, the transfer rate is even
	less than 1Mb/sec!

	Now I would like to ask if any other person has tried to see if
VFFS really improves things.  It seems like, I must be doing something
wrong. 

	I would appreciate if you could tell me how can I improve the
transfer rate.  I need it for digital image processing.

	Thanks in advance!


Muhammad Pervez.


PS:  With ISC 3.0, we have switched to EISA mode.  Before we were
     using our system in ISA mode, and the transfer rate, as measured
     by the above methoed, was about 1.3Mb/sec.  So, contrary to what
     we expected, going to EISA  has made no differece!  (Is there
     any explanation for that also!)

     I tried playing with different 'extent' sizes when creating
     the VFFS. I have tried to vary the extent size from 100Mb to
     1Kb, but it does not seem to make much difference either (
     except that bigger extent sizes waste a lot of disk space!)


                  
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                    <>  Muhammad Shahzad A Pervez <>
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