Performance Effects of Disk Subsystem Choices for VAX** Systems Running 4.2BSD UNIX*

Revised July 27, 1983

Bob Kridle

mt Xinu
2560 9th Street
Suite #312
Berkeley, California 94710

Marshall Kirk McKusick***

Computer Systems Research Group
Computer Science Division
Department of Electrical Engineering and Computer Science
University of California, Berkeley
Berkeley, CA 94720


Measurements were made of the UNIX file system throughput for various I/O operations using the most attractive currently available Winchester disks and controllers attached to both the native busses (SBI/CMI) and the UNIBUS on both VAX 11/780s and VAX 11/750s. The tests were designed to highlight the performance of single and dual drive subsystems operating in the 4.2BSD fast file system environment. Many of the results of the tests were initially counter-intuitive and revealed several important aspects of the VAX implementations which were surprising to us.

      The hardware used included two Fujitsu 2351A ``Eagle'' disk drives on each of two foreign-vendor disk controllers and two DEC RA-81 disk drives on a DEC UDA-50 disk controller. The foreign-vendor controllers were Emulex SC750, SC780 and Systems Industries 9900 native bus interfaced controllers. The DEC UDA-50 controller is a UNIBUS interfaced, heavily buffered controller which is the first implementation of a new DEC storage system architecture, DSA.

      One of the most important results of our testing was the correction of several timing parameters in our device handler for devices with an RH750/RH780 type interface and having high burst transfer rates. The correction of these parameters resulted in an increase in performance of over twenty percent in some cases. In addition, one of the controller manufacturers altered their bus arbitration scheme to produce another increase in throughput.


1.  Motivation

2.  Equipment
2.1.    DEC UDA50 disk controller
2.2.    Emulex SC750/SC780 disk controllers
2.3.    Systems Industries 9900 disk controller
2.4.    DEC RA81 disk drives
2.5.    Fujitsu 2351A disk drives

3.  Methodology

4.  Tests

5.  Results

6.  Conclusions



Appendix A
A.1.     read_8192
A.2.     write_4096
A.3.     write_8192
A.4.     rewrite_8192

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