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a SCSI performance question

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Hi!

Those nice 2nd hand scsi discs get me interested in scsi oncemore! Unfortunately I'm not able to get an answer to my question, although I read many guides: for U160 all devices share those 160mb, ok. If the adapter sits in a 32bit pci slot, I get maybe 85mb through my intel ich5 southbridge, ok.

But what happens if 2 drives on the same channel copy data between them?

Are these data transfered via pci to ram and back to the 2nd drive? Or is the adapter smart enough to directly resend the data?

For my work this would be the main job, working on 1 drive, writing the results to a 2nd one.

Seems 2nd hand Adaptec 29160 cards are cheap enough, so an answer for that one would be highly appreciated. In fact I would appreciate every answer!

Thanks for taking the time! Hannes

PS: my brain says get a 73GB sata raptor, but hey, why that easy ;-))

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IIRC, SCSI can copy direct from drive to drive on the same channel. It's clever like that. Also, going from one channel to another on the same controller, the data will go via the controller, but won't use the PCI bus.

If I'm wrong, someone please correct me!

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The SCSI adapter has no RAM, the SCSI feature for drive-drive copy is not implemented, no OS would ever use it, etc.

You should get 100-120MB/s over PCI on Intel chipsets, enough for two previous generation SCSI drives.

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The problem with what you describe and why it wouldn't work how you wanted is that when you are copying the data between the drives, if you are performing any action on it to modify it in any way, then it would have to be processed through main system memory.

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SCSI is capable of copying direct between devices, however to do so, one device needs to act as Initiator and to the best of my knowledge, no one makes a SCSI HDD with that capability.

SCSI data transfers go from the target deviced to the host system's buffer, and then from the buffer to the destination device. All data transacts through the host system backplane and memory, same as anything else.

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however you system won't come to a screetching halt when doing that compared to ATA

201496[/snapback]

Heck I defrag and move tons of small files around while the rest of my system is still usable. SCSI really has some nice perks.

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Thanks for all your replies! Unfortunatly (?) it seems the adaptec won't fit into my case, so I'm forced ;-)) to get a raptor. Should technically be the better solution as it runs cooler, more silently, even more performance at light load. And cheaper.

@logical1: of course you're perfectly right. It's as easy as you said. Since I modify these files, they simply have to be thrown at the cpu. Thanks for enlightening!

If I think a bit more about it, it seems far more reasonable to get 1 or later 2 raptors. Lower latencies due to direct integration into the southbridge, faster link to memory (AFAIK sata isn't transfered over the pci). The sata drives do not need to share bandwidth.

SCSI would be interesting though.

Thanks for your replies mates! Hannes

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