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February 07, 2011

Need a little 3000 disk? Go to the web

Bos2_cover_sm HP 3000s have a storage legacy to endure: SCSI, the IO interface that HP did not advance for the servers in the prior decade. Finding SCSI replacements for 3000s was supposed to be harder by now. But like any prediction about the death of technology, the reports fall short of reality. You can find what you need on the Web.

Disk drives are the most likely parts of an HP 3000 to fail, being just about the only moving part in the system. (Tape is the other.) Disks from HP are available from independent resellers, but are still more costly than more recent vintages of storage peripheral. When you browse the Web and see a 1 TB disk for $150, you might wonder if there's a chance to use that kind of device in your HP 3000.

By many experts' testimony, there's a good chance that an under-$100 drive will boot up your HP 3000 just fine. These older 3000s use pretty small disks, so the costs of replacement are small, if you go outside HP's inventory. HP stopped selling and making SCSI-2 drives long ago.

If a little drive is all you need, how can you be sure you're buying something that works with the 3000? Years back, John Burke wrote an article for the NewsWire explaining how to do it. HP replied at the time with its set of sensible reasons why the HP-firmwared devices are worth the extra cost. These Low Voltage Device units, long in the tooth, are making homesteading customers look at replacing their 3000 disks that are eight, 10, even 15 years old.

3000 storage experts like Denys Beauchemin have years of evidence that HP's disk standards have not been essential for reliable 3000 service.

I have been using non-HP firmwared disk drives in my HP 3000 for over 10 years now. "SCSI is SCSI," and as long as you can get your hands on a 50 pin SE or LVD disk drive, or if you can get a converter from 68 PIN to 50 pin you should be good to go.

Or if you would rather have something with a newer manufacture date than 1997 (that's so last millennium,) pick up any current (or at least 21st century) LVD-SCSI drive and get a 68-pin to 50 pin converter and have at it.

The converter can be had at granitedigital.com, where Granite Digital Part 6980, 80 SCA to 50m IDC (no termination) runs about $40.

Research on SCSI requirements is best started at the SCSI FAQ. Adaptec's website has good information, too. Allegro's Stan Sieler once posted a comprehensive list of Seagate's disk ackronyms for their drive interfaces. "Seagate drives indicate their interface via the one or two letters at the end of the model number."

LC  Low Voltage Differential, 80-pin SCA
LCV Same as LC, but with an increased cache size
LW  Low Voltage Differential, 68-pin Wide SCSI Connector
LWV Same as LW, but with an increased cache size
N   SCSI, 50-pin Narrow SCSI Connector
DC  Differential, 80-pin Single Connector Attachment (SCA)
ND  Differential, 50-pin Narrow SCSI Connector 

Then, the high-voltage differentials, (HVDs) which can't be used with a simple adapter:
   
W   SCSI, 68-pin Wide SCSI Connector
WC  SCSI, 80-pin SCA (Hot Swapable)
WD  Differential, 68-pin Wide SCSI Connector

So as an example, a Seagate ST318404LC (Cheetah 18GB 10,000 RPM) has a low-voltage (LV) 80-pin interface. Coupled with the converter, it can work with a Series 918 to replace original drives, if you use the original drive cable in the 3000.

Even today, it's simple enough to find a Seagate ST318404LC. Amazon lists the drives new at $74.99

Beauchemin has offered an interesting history of these interfaces:

SE-SCSI is very old (20-plus years) and was almost the original SCSI. It stands for Single-Ended SCSI. Speed is 5 MB/second and the cable can’t be very long, 6 feet or less.

Then came UltraSCSI or HVD-SCSI. The speed was up to 20 MB/second (or even 40, but I’m not sure.) The good thing with HVD is that you could go long distances, 25+ meters with it. It uses the difference in voltages between pins, whereas SE SCSI uses absolute voltages that are very low to begin with. If you remember RS-232 and RS-422, it’s the same principle here. RS-232 was based on signals having a (low) voltage and no voltage and RS-422 was based on the differences in voltage between signal pairs. Which is why RS-232 was certified for 50 feet and RS-422 could go thousands of feet.  It’s all a question of resistance and signal attenuation.

However, it seems that HVD had a speed limit associated with it, perhaps that speed of light thing. Also, as devices became (much) smaller, the need for long distances went down or was better addressed with fiber optics which is insensitive to stray electrical signals.

So, SE came back in vogue, but this time as LVD or Low Voltage Differential. When you plug a single-ended device in an LVD string, all devices, including the host bus adapter, drop down to SE signaling and to the speed of SE-SCSI. So, as long as you can account for the 50 pin to 68 pin thing, either with a cable or an adapter, LVD and SE devices can co-exist, at SE speeds.

LVD hasn't disappeared. Back when Jazz was online at HP, the vendor recommended in a white paper the supplier Rancho SysTech -- which today is still selling adapters to bridge this gap from the 900 Series 3000s that use HVD drives to the more-available LVD drives.

10:47 AM in Hidden Value, Homesteading | Permalink

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