[lug] RH Linux download + hdparm

[John Karns]

On Thu, 18 Oct 2001, Sexton, George said:

> Which brings up a really under appreciated point. Just because the interface
> is rated at a certain speed it doesn't mean the drive can do anything like
> that kind of speed on sustained reads or writes.
>
> A good example is Ultra-160 SCSI drives. Generally, the drives cannot read
> or write more than 20-25MB second. Period. End of sentence. Look at the
> sustained throughput rate specification if you want to find out what you can
> realistically do with a drive.

My understanding is that the theoretical maximum bw on a PCI controller is
around 33 MB/s, due to the design spec of the PCI bus itself.  Someone
please correct me if I'm mistaken.  Thus the main advantage in U-160 SCSI
drives is in a RAID configuration where the data passes from hdd to hdd
via the controller.  My assumption is that in this situation, the SCSI
controller would not need to use the mobo's DMA controller chip.  Again,
someone please correct me if I'm wrong.  For this reason I figure I'm just
as well off with the cheaper Ultra-Wide 40 MB/s drives.

----------------------------------------------------------------
John Karns                                        jkarns at csd.net