rdh@sli.com (Robert D. Houk) (08/13/90)
As I was replacing one of our Wren-V disks yesterday, going through the
jumpers, I was reminded of a puzzle: What is the purpose of the Parity
Jumper? All of the disks come with the jumper removed, and the manual is
delightfully terse on what it actually does. I assume installing the
jumper enables parity checking? On disk Data? SCSI Data? Time of Day?
If Parity is not enabled (no jumper), does the disk use ECC (standard
features include "48 bit ECC polynomial" Error correction). Conversely,
does installing the parity jumper disable some other/better error checking
hardware/firmware? Does Parity slow the [effective speed of the] disk down
or use more bits on the disk to encode parity, thus lowering the total
storage capability?
In other words, for most reliable operation of the disk, should the parity
jumper be installed or removed?
-RDH
--
A buddhist nudist RDH@SLI.COM | uunet!sli!rdh
practices yoga bare. Robert D. Houk
Software Leverage, Inc.
485 Massachusetts Avenue
Arlington, Mass. 02174kirchner@informatik.uni-kl.de (Reinhard Kirchner) (08/14/90)
From article <RDH.90Aug12150533@borodin.sli.com>, by rdh@sli.com (Robert D. Houk): > As I was replacing one of our Wren-V disks yesterday, going through the > jumpers, I was reminded of a puzzle: What is the purpose of the Parity > Jumper? All of the disks come with the jumper removed, and the manual is > delightfully terse on what it actually does. I assume installing the > jumper enables parity checking? On disk Data? SCSI Data? Time of Day? When I installed my WREN-Vs in the fileserver I also got to this point. So I phoned the distributor and they told me, the parity on the cable is enabled. So it may be of use if there is a host adapter which generates and checks parity on the cable, but I think most do not. They don't have jumpers for this ! R. kirchner Univ. of Kaiserslautern, Germany
colin@array.UUCP (Colin Plumb) (08/15/90)
The parity jumper enables parity checking on the SCSI bus; parity generation is always on. If your system will run at all with parity checking enabled (i.e. everyone generates it properly), you should leave it enabled. I know it completely eliminated some minor flakiness I was experiencing. BTW, from my WREN-V OEM manual, there are 7 positions on the jumper strip. Starting from the side closest to the 50-pin SCSI connector, they are: 1) Parity Enable (plugged in = checking turned on) 2) Motor Start Option (plugged in = motor will not turn on until Start Unit SCSI command received; otherwise it will start on power-up) 3) SCSI ID bit 0 (value = 1) 4) SCSI ID bit 1 (value = 2) 5) SCSI ID bit 2 (value = 4) The last two positions select terminator power. The pin on the far end, away from the PC board, supplies power to the terminators. If it is horizontal, power is taken from the TERMPWR line on the SCSI cable. If it is vertical, power is taken from the drive internally. The pin in position 6, closest to the PC board, is not connected. -- -Colin
lampi@polari.UUCP (Michael Lampi) (08/16/90)
In article <6399@uklirb.informatik.uni-kl.de> kirchner@informatik.uni-kl.de (Reinhard Kirchner) writes: >From article <RDH.90Aug12150533@borodin.sli.com>, by rdh@sli.com (Robert D. Houk): >> As I was replacing one of our Wren-V disks yesterday, going through the >> jumpers, I was reminded of a puzzle: What is the purpose of the Parity >> Jumper? ....[rest deleted for brevity] >So I phoned the distributor and they told me, the parity on the cable >is enabled. So it may be of use if there is a host adapter which generates >and checks parity on the cable, but I think most do not. They don't >have jumpers for this ! > Many host adapters and host systems support parity on the SCSI bus, including Apollo, Adaptec, Western Digital and others. Considering that the only means of detecting transmission errors in a non-parity checking system is by verifying data read or written to a peripheral through some sort of error- correcting code which would tie up more storage space and slow things down immensely, parity is a cheap and easy way of reducing the possibility of errors. Of course, if you don't mind 'slightly' incorrect data, then you don't need error checking :-) ! Michael Lampi
chris@com50.c2s.mn.org (Chris Johnson) (08/17/90)
In article <RDH.90Aug12150533@borodin.sli.com> rdh@sli.com (or uunet!sli!rdh) writes: >As I was replacing one of our Wren-V disks yesterday, going through the >jumpers, I was reminded of a puzzle: What is the purpose of the Parity >Jumper? All of the disks come with the jumper removed, and the manual is >delightfully terse on what it actually does. I assume installing the >jumper enables parity checking? On disk Data? SCSI Data? Time of Day? Jumper installed enables of parity checking of the data bits DB0 - DB7 on the SCSI bus. Wren drives always generate parity on the SCSI bus, but only check it if the jumper is installed. Disk data parity and ECC is always generated and checked, internally. -- ...Chris Johnson chris@c2s.mn.org ..uunet!bungia!com50!chris Com Squared Systems, Inc. St. Paul, MN USA +1 612 452 9522