HP 9000
cancel
Showing results for 
Search instead for 
Did you mean: 

Correct type of SCSI cable for L2000 to external SCSI tape drive

SOLVED
Go to solution
EEESEC
Frequent Advisor

Correct type of SCSI cable for L2000 to external SCSI tape drive

Didn't realize there were so many different types of SCSI cables.

I have an L2000 (rp5450) that has, according to the manual, a core I/O with an Ultra-2 SCSI Connector (68-Pin VHDCI SCSI). This is connecting to a Smart DDS-3, External DAT "desktop" drive, 12-24GB, SCSI - pictured here:

http://www.pacificdatastorage.com/c6364a.asp

The tape drive has two scsi connections on it. We daisy chain another tape drive to it using the other free scsi port. On the scsi tape drive it reads only "single ended scsi".

Using "cablestogo" as a reference, can any cable guru suggest the best cable to use for
1. the connection from the core scsi connector on the server to the tape drive

And if different

2. the connection from one tape drive to the other

Cablestogo search:
http://search.cablestogo.com/?vno=48&Ntt=scsi+cable&N=0

We have one confirmed cable failure so need to replace and want to get a few spare. Would be nice if I ordered the right ones on the first try.

Thanks!

 

 

P.S. This thread has been moved from General to HP 9000. - Hp Forum Moderator

10 REPLIES
Steven E. Protter
Exalted Contributor

Re: Correct type of SCSI cable for L2000 to external SCSI tape drive

Shalom,

Note: Don't plan on using this tape drive for Ignite make_tape_recovery . It is not on HP's list and I would not rely on it for Ignite based DR.

I worked for years with this class server. The default SCSI connector on it is LVD.

I would not daisy chain two tape drives on the same scsi card even it were possible. I/O issues are likely.

As far as the cable buy goes, I'd pay the outrageous price and get them from HP hardware, at least then they are guaranteed to work with the SCSI card and sytem.

SEP
Steven E Protter
Owner of ISN Corporation
http://isnamerica.com
http://hpuxconsulting.com
Sponsor: http://hpux.ws
Twitter: http://twitter.com/hpuxlinux
Founder http://newdatacloud.com
Steven Schweda
Honored Contributor

Re: Correct type of SCSI cable for L2000 to external SCSI tape drive

> I would not daisy chain two tape drives on
> the same scsi card even it were possible.
> I/O issues are likely.

Like what, for example? Why do they put two
connectors on the drive instead of one? Why
have more than two SCSI ID values?

> [...] I'd pay the outrageous price [...]

I wish I had your budget. I tend to use
cheap cables (from Ebay or a local junk
store) which have the right ends and
something resembling wire in between. If
you already have one good cable, then you
know what the right one looks like. You
should look for a cable which is not too
long, and which is rated for the speed at
which the bus will be operating. I'd expect
a 20-year-old cable to have trouble at
Ultra320 speeds, for example.
EEESEC
Frequent Advisor

Re: Correct type of SCSI cable for L2000 to external SCSI tape drive

Thanks for the quick reply.

They've been using this setup for over 5 years and it works... ok. I wouldn't suggest it either but we are kind of stuck with it for now. (We are getting blades with an EVA soon to replace the system.)

I was trying to avoid the 400% or more markup for a cable that has an HP stamp on it. Save the taxpayer a few bucks.
EEESEC
Frequent Advisor

Re: Correct type of SCSI cable for L2000 to external SCSI tape drive

Just to be sure, "LVD" is also synonymous with "scsi-3" and "ultra-2" right?
EEESEC
Frequent Advisor

Re: Correct type of SCSI cable for L2000 to external SCSI tape drive

After more research what I've found is that I need is a 68 pin VHDCI "mini-centronics" male to a 50 pin mini-centronics male.

To elaborate on why our SCSI tape drive setup doesn't work very well is that the SCSI bus for the tape drives and hard drives are shared. Two hard disks also use the bus at 0/0/1 along with the tape drives. If the system is running at a high load the tape drives sometimes hang and fail.

Haven't heard of any issue regarding the daisy chaining other than if you are using both tape drives at the same time the above issue could occur more frequently I guess.
Matti_Kurkela
Honored Contributor
Solution

Re: Correct type of SCSI cable for L2000 to external SCSI tape drive

LVD was introduced in 1998, along with Ultra-2.

SCSI-3 was introduced in 1996, before LVD, so it would be sensible that all LVD devices would also be SCSI-3 compliant. But the world of SCSI is not always sensible.

As your other tape drive says "Single Ended" (SE), it's something of a problem. The presence of SE devices on a LVD bus shouldn't break anything, but *will* cause the speed of the entire bus to drop to SE levels: goodbye Ultra2.

The SE bus length restrictions will also be in effect. In Ultra/UltraWide speeds, the SE total bus length limit is only 1.5 m, so this might easily become a problem.

(Disclaimer: that information comes from my old notes, which might be incorrect.)

MK
MK
Steven Schweda
Honored Contributor

Re: Correct type of SCSI cable for L2000 to external SCSI tape drive

> [...] Two hard disks also use the bus at
> 0/0/1 along with the tape drives. If the
> system is running at a high load the tape
> drives sometimes hang and fail. [...]

I'd expect poor performance and wasted tape,
bit not an actual I/O error. (But what do I
know?) I'd certainly look into getting
another SCSI adapter in there, and moving the
tape drives onto it.

> The SE bus length restrictions will also be
> in effect. [...]

And that could explain some things. It's not
very easy to get internal disks and a couple
of external tape drives onto a cable within
the length limits. (1.5m sounds familiar to
me, too.) A too-long cable with a busy bus
could account for a variety of problems.

Cheap SCSI cards can be found on Ebay, too.
EEESEC
Frequent Advisor

Re: Correct type of SCSI cable for L2000 to external SCSI tape drive

First, I disagree with whoever moved this thread to the storage section. This issue is not particular to storage and I may get fewer pertinent responses b/c of this.

As your other tape drive says "Single Ended" (SE), it's something of a problem. The presence of SE devices on a LVD bus shouldn't break anything, but *will* cause the speed of the entire bus to drop to SE levels: goodbye Ultra2.

So you are saying that when these tape drives are attached the entire bus, including the two hard drives, are throttled back to SE "SCSI 2" speeds? That's nuts. They've been using this config forever. I'm going test drive speeds with and without, though I have no doubt you are right.

The wiki on SCSI looks to have a good comparison table:

http://en.wikipedia.org/wiki/SCSI

What I think we have is an Ultra2 Wide SCSI bus (row 7) which it states has a bandwidth of 80 MB/s going to a "Fast SCSI" (SCSI -2) (row 2) device that has a bandwidth of 10 MB/s. The bus will default to the specs of the lower standard, including a maximum length of 3m. Is this agreed?

Thanks for all the great replies. Very good info.





Steven Schweda
Honored Contributor

Re: Correct type of SCSI cable for L2000 to external SCSI tape drive

> [...] That's nuts. [...]

But that's what I'd expect, too. Another
pretty good reason to get those tape drives
onto a different SCSI bus.

I have dim memories of Solaris sending a
message to the console during system start-up
when a SCSI adapter negotiated a speed
reduction. I don't know if HP-UX does
anything similar, but it might be worth a
look.
EEESEC
Frequent Advisor

Re: Correct type of SCSI cable for L2000 to external SCSI tape drive

closed