Matthew Dillon wrote:
>
> The standard PCI bus can do 130 MBytes/sec. Even with overhead issues
> (setup for a DMA burst) it can still do 100 MBytes/sec.
But that depends on what is also going on at the same time. There are
three other cards in my PCI bus. You can eliminate one because I
wasn't using the sound card :).
>
> A standard SCSI controller can do 40, 80, and now even 160 MBytes/sec
> over the wire - standard copper cabling w/ LVD connectors (example
> below).
This is where the cache size on the HD becomes important. It also acts
like a hardware double buffering.
>
> A modern hard disk can do 10-30 MBytes/sec to/from the platter, assuming
> no seeks. But the moment it needs to seek the performance drops
> drastically ... generally down to 1-5 MBytes/sec.
I haven't seen any 30MB/s. The 10K LVD IBM's were just about the
fastest at 20MB/s continuous. The drop for UDMA drives is to even
lower rates.
>
> So in the case of a file copy over a SCSI bus, the physical disk is
> almost always going to be the limiting factor.
I just noticed that mine isn't showing "Tagged Queueing Enabled" is
that something I can set? The adapter is an Adaptec 2940uw.
da0 at ahc0 bus 0 target 4 lun 0
da0: <IBM DCAS-34330W S65A> Fixed Direct Access SCSI-2 device
da0: 40.000MB/s transfers (20.000MHz, offset 8, 16bit)
da0: 4134MB (8467200 512 byte sectors: 255H 63S/T 527C)
Kent
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Kent Stewart
Richland, WA
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