U320 Cable Lengths

Leon Toh tltoh at attglobal.net
Fri Aug 29 01:25:14 PDT 2003

* From the T10 Reflector (t10 at t10.org), posted by:
* Leon Toh <tltoh at attglobal.net>
Thanks for the information.

Multidrop cable which I have been using has a spacing of about 10 - 11 
inches apart between connectors. Cable core is twisted and shielded at the 
same time. Terminator is also supposably U320 compatible. What kind of 
cable did you ended up using ?

I can tell you what makes my job a real nightmare and these are the people 
who I have to with on a daily basis unfortunately. A lot of system 
integrators and assemblers out there are using cheap cables and terminators 
which they source from suppliers who then source them from places like 
Taiwan and China. I have already seen a number of cables and terminators 
which supposably to be U320 but it's characteristic is no where near there 
at all. When there is an issue they blame either the HBA or HDD being the 
fault but never the cheap cable or cheap HDD blackplane which they happen 
to be using.

Best Regards,

At 08:56 PM 25/08/03, Aloisi, Paul wrote:
>Ultra320 SCSI requires different cables and spacing than Ultra160 or Ultra2
>SCSI. Unfortunately the PIP and SSM standards were not ready when Ultra320
>was released. The successful multidrop cables that I have used for Ultra320
>and Ultra640 testing were based on 5 1/4 inch spacing between flats with the
>connectors placed at 2 or 3 flats apart, alternating the spacing. The 9.85
>inch spacing used for Ultra160 and Ultra2 are actually a filter for the
>Ultra320 and Ultra640 speeds. Most backplanes had to be redesigned for
>different spacing, many of the backplanes had the same problem as the
>cables, creating a filter for the Ultra320 and Ultra640 speeds.
>What helps a lot of these system is to drop the terminator impedance, if you
>used the SPI-5 terminator for Ultra320 systems and drop the impedance to
>minimize the reflection from the terminator, this will help a lot on
>backplanes with close spacing.
>The SPI-5 standard refers to both PIP and SSM-2 standards, these are all
>published standards. If you used the SPI-5 documentation for Ultra160,
>Ultra320 and Ultra640 systems, you will get much better results.
>Unfortunately the programmable terminator, PIP and SSM-2 were not ready when
>we released SPI-4, which first documents the Ultra320 speed.
>Thank you,
>Paul Aloisi
>-----Original Message-----
>From: Leon Toh [mailto:tltoh at attglobal.net]
>Sent: Monday, August 25, 2003 2:03 AM
>To: t10 at t10.org
>Subject: Re: U320 Cable Lengths
>* From the T10 Reflector (t10 at t10.org), posted by:
>* Leon Toh <tltoh at attglobal.net>
>U320 have been a real nightmare and it still is for many of us. My
>experience here are mostly with U320 HDD in RAID environment.
>Once I have 4 or more U320 HDD attach to a multi-drop cable I start having
>nightmares. At most times with 4 U320 HDD I find that the HBA will
>negotiate reliably for most of the HDD at U160. If I wanted U320
>reliability than I have to take a number of factors into consideration. For
>me I find that the type of multi-drop cable and cable quality happens to
>play a major role besides HDD firmware when comes to U320 negotiation
>As you mention that the specs specifies that for a multi-drop configuration
>maximum allowed cable length is 12.5 m. To me this is virtually impossible
>going by the number of issues which I have encountered. By the way we are
>also having issues when comes to hotswap passive backplane using U320 HDD's
>Majority of the issues I'm experiencing here I would say they are mostly
>noise related. Reason I got to this conclusion was mainly the fact that
>there is no consistency at all and in some instances using the same
>multi-drop cable, HDD and HBA but install into a completely different
>Server / Workstation sometimes it work reliably for me.
>I hope that HDD vendor's won't be releasing a U640 parallel version when
>the specs is finally finalise. Otherwise I can imagine the amount of issues
>we would face when parallel U640 version becomes available.
>Best Regards,
>At 09:25 AM 23/08/03, Kevin D Butt wrote:
> >I have a question about real-world cable lengths in use in Ultra 320
> >environments.  SPI-5 lists the cable lengths at 25 m for point-to-point
> >and 12,5 m for multi-drop.
> >Is there anybody out there who is actually using 25 m cables in point to
> >point without any issues?
> >Is there anybody out there using 12,5 m cables with mulitple devices
> >attached without any issues?
> >How many devices have successfully been used on one cable?
> >
> >Thanks,
> >
> >Kevin D. Butt
> >Fibre Channel & SCSI Architect, IBM Tape Microcode,
> >6TYA, 9000 S. Rita Rd., Tucson, AZ  85744
> >Tie-line 321; Office: 520-799-5280, Lab: 799-5751, Fax: 799-4138, Email:
> >kdbutt at us.ibm.com
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