U320 Cable Lengths

Leon Toh tltoh at attglobal.net
Fri Aug 29 02:21:15 PDT 2003


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

 Kevin,

 I'm fairly certain that some of the HBA and HDD guy's just to name few like Adaptec, LSI, Intel, HGST and Seagate would be able to shed some lights as I happen to know that they have encountered a number of initial U320 issues and had carried out some research into it back at their lab.

 I have done a few complete U320 external installation. I also encountered some issues and it all depend's on the type of drive enclosures and configuration I had with the drive enclosure. Typically using a 1 metre in most of my installation instances I can get U320 speed. As Paul indicate by varying the impedance we can use a longer cable length as I found if I change the drive enclosure backplane from single to a split configuration. 

Unfortunately I have not done any U320 work with tape libraries or tape drives as I haven't came across any of them at this stage. However I have done quite a few work base on U2 and U160 tape drives and library and not much of a nightmare for me at all.

 Hope this is of some help to you.

 
Best Regards,
 Leon

 At 03:28 AM 26/08/03, Kevin D Butt wrote:
 Paul and Leon, 

Thanks for your responses, this gives me a lot to think about.  It appears that your notes relate specifically to HDD and RAID type of devices.  Do you have any experience related to external cabling? 

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 


;Aloisi, Paul; <paul_aloisi at ti.com> 
Sent by: owner-t10 at t10.org 

08/25/2003 03:56 AM 
        
        To:        ;'Leon Toh'; <tltoh at attglobal.net>, t10 at t10.org 
        cc:        
        Subject:        RE: U320 Cable Lengths 



* From the T10 Reflector (t10 at t10.org), posted by:
 * ;Aloisi, Paul; <paul_aloisi at ti.com>
 *
 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 
reliability.

 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 
also.

 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,
 Leon

 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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