BlueSCSI – Open, Low Cost, DIY SCSI to SD Device

Re:BlueSCSI – Open, Low Cost, DIY SCSI to SD Device – Tinker... by rsync on Saturday December 11, 2021 @01:22PM (#29523009)

Wouldn't a SCSI <--> SATA device be much more performant and useful ?

Which is to say, one would attach a 2.5" SSD as the SATA device rather than a SD device ...

I have such an adaptor:

http://www.acard.com/index.files/Page613.htm

... although I am not sure if they are produced anymore.

I am also not sure if there is any point at all in discussing the relative speeds of SD vs. SSD when the bottleneck at the end is 50pin SCSI ...

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Re:BlueSCSI – Open, Low Cost, DIY SCSI to SD Device – Tinker... by Maursault on Saturday December 11, 2021 @01:34PM (#29523099)

> Wouldn't a SCSI <--> SATA device be much more performant and useful ?

No. BlueSCSI and other SCSI device emulators are intended for use with SCSI-1 (narrow) and SCSI-2 (fast) controllers, maybe even Wide SCSI-2 (fast wide) for some, so the maximum bandwidth here is 5, 10 and 20 MB/s, respectively. Secure Digital is a pretty good match for bandwidth and in many if not most cases saturates the bus. Even if you had a SCSI to NMVe SSD adapter, it would never perform faster than the old bus it's running off.

> I am also not sure if there is any point at all in discussing the relative speeds of SD vs. SSD when the bottleneck at the end is 50pin SCSI ...

Sometimes the bottleneck is the CPU. In some popular vintage classic machines, on a very good day, the bandwidth of the RAM is almost 15MB/s.

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Re:BlueSCSI – Open, Low Cost, DIY SCSI to SD Device – Tinker... by rsync on Sunday December 12, 2021 @12:48PM (#29531731)

A followup:

It turns out the devices I have are this one:

Addonics ADSALVD160

... which I believe are no longer in production. It is LVD160 on one side and SATA on the other. It has a floppy-sized molex power connector on the board.

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Re:BlueSCSI – Open, Low Cost, DIY SCSI to SD Device – Tinker... by Maursault on Sunday December 12, 2021 @04:33PM (#29533844)

I believe your insinuation to be factual, that you can use that adapter to connect a standard SATA drive to a scsi bus, since ultra160 is backwards compatible. But whatever the bandwidth of the bus your converting down to, depending on processor speed, that will be the bandwidth you see, so it's still down to what was available on logic boards and NuBus cards, only narrow, fast and fast wide scsi, topping out at 20MB/s (unless there is an Ultra SCSI NuBus card out there for 40MB/s). Your adapter would be pretty useful for later vintage PCI machines, because you can probably find an Ultra160 PCI card.

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Re:BlueSCSI – Open, Low Cost, DIY SCSI to SD Device – Tinker... by rvense on Saturday December 11, 2021 @01:48PM (#29523223)

AFAIK no old Mac will do 5MB/s on its built-in, external SCSI.

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Re:BlueSCSI – Open, Low Cost, DIY SCSI to SD Device – Tinker... by Maursault on Saturday December 11, 2021 @01:56PM (#29523286)

That's the maximum bandwidth for narrow SCSI-1, used in anything from Mac Plus to 68030 machines. The external SCSI, a separate bus, is always SCSI-1. Sometimes the internal SCSI is SCSI-2 (some 68040 & PPC Macs). WGS95 had a wide SCSI card (so had 3 separate SCSI busses, narrow, fast, and fast wide).

Reportedly, with any of the SCSI emulators, it is not difficult to saturate a narrow SCSI bus with a 68030 Mac, so... it will do exactly 5MB/s on narrow SCSI in these cases.

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