SCSI, LVD, etc... ?

Daemonfly · Aug 13, 2003

My Compaq server can has 3 68-pin Wide Ultra2/Ultra3 SCSI channels with an LVD interface, and I'm trying to find what drives I can use with this.

Whats the details on LVD - mainly what types of drives will work with my setup?

From www.scsita.org : SPI-2 doubles the speed again to Fast-40 commonly know as Ultra2 SCSI, 40 megatransfers per second or on a wide bus 80 megabytes per second with a new electrical interface, low voltage differential, LVD SCSI. Single ended can not be used for speeds above Fast-20. The SPI-2 standard included SIP, the Single Connector Attachment (SCA-2) 80 pin Host swap connector and the 68 pin Very High Density Connector (VHDCI). The SCSI-2 A and SPI P connectors are include in SPI-2.

This seems to say that all Ultra2 are LVD

Do I have to get only drives listed as LVD, or can I use any Ultra2/3 SCSI drives?

Also, is there any loss of performance from going from converting a 68-pin connection to a 80-pin drive? I'm guessing not.

I've found some very cheap wide Ultra-2 & Ultra-3 Seagate 80-Pin drives that I'd like to get (why is 80-pin so much cheaper than 68-pin??!?!) . Some list LVD in their specs, but others(cheaper) I were considering list ASA2 (seems to be a Seagate-only architecture).

stool · Aug 13, 2003

Ultra2 and 3 are, on the whole, LVD drives. I can only guess that the 80-pin drives are cheaper due to age(older models, perhaps). There is no performance loss. All cables that I have seen come with the 68-pin connectors as standard.

Another ineresting and informative site for you can be found here; http://scsifaq.paralan.com/

Caffinehog · Aug 13, 2003

I thought the 80-pin drives were for hot swap and the 68 pin drives were not. I'm pretty sure you need a proprietary server platform to do this, though.

In any case, you can snag adaptors for 80 to 68 pin on ebay and on several electronics sites.

Daemonfly · Aug 13, 2003

Nice link! - I'll have to read that whole page tonight at work.

From what I found on that site you linked, it seems the the drives have the SCA connectors:

Q. 27. I recently purchased a new SCSI drive with an SCA (or SCA-2) connector. How do I connect this to my cabled SCSI system?
Answer: The SCA (and its derivative SCA-2) connector is used on disk drives that are meant to be used in a SCSI backplane. It is an 80-pin connector that contains the same 68-pins as the "standard" 68-pin high density SCSI connector plus several power supply pins, a number of pins for control signals and pins to set the SCSI address of the drive. I are not aware of any mating cable connector being available, and if it is, I am sure it is extreme unwieldy.

The best way to handle this situation is to take the drive back and exchange it for one that has the standard 68-pin high density SCSI connector. Most SCSI LVD and faster drives are available with either connector. If exchanging the drive is not an option, you can get an SCA to 68-pin or SCA to 50-pin adapter to plug into the SCA connector on the drive that will provide a standard SCSI cable connector (68-pin or 50-pin), a connector for powering the drive and settings for the drive ID. Some even offer selectable termination. If you buy an adapter like this, make sure that the termination is correct for the drive you have. You should be able to find a number of sources for these adapters on the Internet.

You should be aware that an SCA to SCSI adapter adds a lot of capacitance to the SCSI cabling, so you should use no more than 2 of these adapters in any given SCSI bus segment.

I was planning on quite a few of them, and getting adapters, but that capacitance problem gets in the way. Perhaps I'll still get them and go with an external enclosure or two that have that 80-pin SCA backplane if I can find them cheap enough.

Xaotic · Aug 13, 2003

Generally, there is no speed degradation with using the adapters. Make sure that you get those specified for U160/320 operation for future compatibility though.

The 80 pin drives are cheaper as they're produced in much higher quantities for hot swap racks for servers, workstations and expansion units.

ASAII seems to refer to the firmware on the drives, rather than the drives themselves. They'll use 68pin LVD/SE connectors and be very slow. The drive listed for this range are suitable for storage, if you have lots of physical space available. I would recommend against using them for any high I/O level devices. I'd probably be somewhat paraniod about data safety due to age as well. This is one that seems to be one model that's currently being offered and it's no speed demon, 5400RPM and a 13.2ms seek.

http://www.seagate.com/support/disc/scsi/st446452w.html

If that were one being considered, I'd recommend getting at least 7200RPM and preferrably 10K rotational speeds, even if you had to save for additional drives.

Daemonfly · Aug 13, 2003

It's mainly for storage. Was thinking of picking up a bunch of 10k 80-pin since they were cheap. Now I realize I'll only be able to use them if I get a hotswap enclosure.

I still needed to know the deal with the LVD though, that was my main concern. This server only has 3 9.1G drives in it now

Bender · Aug 13, 2003

You can still buy the 80 pin drives for your current system. All you need is an SCA 80>68 pin adapters. Ebay is a great place to look as long as you know what your looking for.

druidelder · Aug 13, 2003

68pin>80pin adapters can run you anywhere from $5-20 each. You can usually find one or two at lower prices, but if you need several it can be hard to find several at the same time for the lower prices. The adapter also has the power plug (you'll note that there is no power connector on the back of 80pin drives).

Xaotic · Aug 13, 2003

There are also jumpers on the adapters to set SCSI ID and some other functions normally controlled by the backplane.

Daemonfly · Aug 14, 2003

Ebay has 7-bay Compaq Storage servers(minus trays) for $30+ S/H. Figure I'd just be better off getting one or two of these than buying a bunch of adapters. Hell, 7 adapters would be at least $35...

Since I can do 15 drives per channel, could I fill one 7-bay rack, set it's IDs at 1-7, then chain that to another 7-bay rack and set that for 8-14, leaving card at 0 for the external connector?

stool · Aug 14, 2003

I recently had one of the Compaq server storage rigs, and they usually work great. One caution, though. Some of the older cheaper ones aren't set up for LVD, so you'll have to verify that before you buy. Also, try to get one with the trays, as it greatly simplifies matters as far as hot swaps.

SCSI, LVD, etc... ?

Daemonfly

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