LVD Ultra2 SCSI, can it fry a drive?

[Moe]

Hello, this is probably a very ignorant (stupid) question, but here goes,

Can using a non LVD (Low Voltage Differential) Drive with a LVD adapter (adaptec 2940u2w) cause damage to anything?

I've just recently bought a drive that supports SCSI3 160 with a 68 pin High Density port, and I'm not sure if the drive (Quantum Atlas 10K) is LVD compatible or not.

I believe that it is, but I don't want to do anything foolish with a pricey drive.

Thanks.

[FastEddie]

I've been lookin' at this drive with great interest. I already run a pair of LVD Viking II's on an AHA2940U2W and have been pleased with their performance and stability.

The Atlas 10K comes in two flavors, 80-pin SCA and 68-pin LVD. The Atlas 10k you picked up is an LVD drive and fully backward compatible with Ultra2 standards. It also has an SE (single-ended) jumper setting to enable the drive to be used on an UW controller as well.

FTL to http://online1.quantum.com/support/hdd/atlas10kw_scsi_support.htm where you will find the info I've referred to.

FastEddie

[MadMax]

Doesn't matter if the drive or the cntrlr is lvd capable or not. There is no compatibility issue here....

www.seagate.com/support/disc/faq/ultra2_scsi_lvd.shtml#6 (http://www.seagate.com/support/disc/faq/ultra2_scsi_lvd.shtml#6)

HVD requires a special bus but LVD is backward compatible both ways (from the bus AND from the devices)

Keep in mind that if you install a non-lvd disk on your lvd bus, lvd will be disabled for the entire bus. SCSI will use the bus standard for the oldest bus architecture in use on a given bus.

If you have the Ultra160/m, then you have an lvd supported drive. Lvd is standard with that bus architecture.


fast eddie~The Atlas 10K is available with 5 different bus options. There is more than one bus with 68 pin connections(Atlas 10K is available in three 68 pin formats). Only Ultra2 and Ultra160/m support lvd. Ultra does not! The other two are 80 pin and fiber channel. online1.quantum.com/products/hdd/atlas_10k/atlas_10k_overview.htm (http://online1.quantum.com/products/hdd/atlas_10k/atlas_10k_overview.htm)




[This message has been edited by MadMax (edited 07-15-99).]

[Moe]

Ok thanks for clearing that up for me.

A friend of mine said that using an LVD controller with a non-lvd drive would be disasterouts, but now I think he must have meant HVD not LVD.

About what MadMax said, I think that you can have two SCSI segments on the Adapte2940U2W that will allow one to use both LVD and non-LVD devices by having the LVD connected to that connector, and the other (50-pin) devices on the other connector with interal termination disabled on the adapter. Is this a possible configuration?


So, FastEddie, what kind of sustained transfer rates do you get with those Vikings?

[This message has been edited by Moe (edited 07-15-99).]

[FastEddie]

CYM Moe. I'll dl a few other bench programs.

As for the 2940U2W with only internal devices installed, you are right, except for the controllers termination. When you run only internal devices, then keep the controller terminated. If you mix internal with external devices, then disable the controllers termination.

FastEddie

[MadMax]

Ah, yes....
Split segments.
The bottom line with that is you create an entirely seperate bus with a common adapter. Control bits never overlap, therefore you have unique data/control paths and hence, two seperatebus paths with no need to route common SCSI protocol.

If you access both segments simultaneously, say goodbye to the max transfer rate of the faster segment...That type of architecture will choke your high dollar ultra2/lvd devices/capabilities. Why shell out huge $$$ on state of the art SCSI tech if you're going to attach an anchor to it?

[Moe]

Really?? I was under the impression that the LVD segment would operate at the speed of the slowest device on its segment, and the other segment would operate at the speed supported by the slowest device on it's segment.

So, are you saying that the LVD segment would drop to the speed of the other segment if both segs are being used at the same time? Wow, that would slow things down.

My only consolation is that the max sustained transfer rate for my drive is from 18-26 MB/sec. . .

Again, SCSI reveals its mysteries to me at a delayed pace.

[MadMax]

Yes. Xfer rates will be reduced in the lvd segement. Not necessarily all the way down to the xfer rate of your slowest device on the secondary segment but substantially lower, nonetheless.

This split segment idea was incorporated to allow the user to utilize the greatly increased bus length capabilities of lvd without totally eliminating backward compatiblilty. The controller must still regulate data speed according to the slowest device that it controls during a multiple device xfer. Remember, this ONLY occurs during SIMULTANEOUS device access. Your controller can and does assign data speeds accordingly when cross segment data xmit/rcv requests are not occuring. A significant improvement over previous models.

The only way to completely eliminate this problem is to put slower devices on seperate controllers, same as before.

[This message has been edited by MadMax (edited 07-17-99).]

[Moe]

This is an interesting little tidbit about what Adaptec says on their site about this for the AHA-2940U2W (below)


Assured Ultra2 Performance
With SpeedFlex Technology
[top of page]

The SCSI Card 2940U2W features SpeedFlex technology which ensures
the most performance from Ultra2 peripherals by creating two
electronically isolated SCSI bus segments on the card--an Ultra2
segment and an Ultra SCSI segment. These two segments enable the
SCSI Card 2940U2W to simultaneously operate at both Ultra2 SCSI and
Ultra SCSI speeds. With SpeedFlex, the board can support Ultra2
peripherals at speeds up to 80 MByte/sec on the Ultra2 SCSI bus
segment, while simultaneously supporting Fast and Ultra SCSI devices
at speeds up to 40 MByte/sec on the Ultra SCSI bus segment. Without
SpeedFlex technology, any Fast or Ultra SCSI peripheral connected to
an Ultra2 SCSI bus will drop the maximum burst rates of all peripherals
on the bus to the Ultra SCSI performance level.

Yep, its ambiguous as hell. This was very confusing for me before MadMax cleared this up.

Its something to think about at least...

Thanks Fasteddy and MadMax for all of the help.

[This message has been edited by Moe (edited 07-18-99).]

[MadMax]

Yup, even a quality company like Adaptec still employs lousy marketers that can't seem to mention anything but what their products CAN do. Notice the hype-add here doesn't mention cross-segment activity, a common occurance.......

A lie by omission is still a lie. http://www.sysopt.com/forum/frown.gif

I hate marketers with a passion.