[lug] RH Linux download + hdparm

[D. Stimits]

John Karns wrote:
> 
> On Fri, 19 Oct 2001, D. Stimits said:
> 
> > I forget how it is figured out, but a regular PCI bus is 33 MHz, not 33
> > MB/sec. The bus is 4 bytes/octets wide (32 bit), so that means at least
> > 4 * 33 = 132 MB/sec. In my case, I'm operating on a 66 MHz, 64 bit bus,
> > so the minimum rate would be 4 times that. U160 is nice even on a
> > regular 33 MHz PCI bus, but peak rates or the rate of a good raid
> > controller could saturate the bus under normal PCI.
> 
> Thanx for the response.  But I'm not too sure about the gains.  I'm
> running a U160 drive with an ultra-wide (40 MB/s Tekram 390U) controller
> on an Asus P5A mobo (33 Mhz PCI, 500Mhz K6-II cpu).  hdparm says I'm
> getting 15 MB/s.  I had been wanting to order a U160 controller to replace
> the 390, but under the circomstances, I'm afraid that it could be a waste
> of $$.  Perhaps I'll try a quick benchmark with an Adaptec 2940UW for
> comparison to see if it's a controller issue.

If your drive only runs 15 MB/s, you wouldn't have much to gain. The
exception is if your PCI bus is already bandwidth challenged by some
form of i/o, then the burst rate would be very helpful. SCSI, unlike
IDE, is rather intelligent, and you don't generally worry about things
like DMA settings. On the actual SCSI cable, devices can get
instructions and then detach until they have something to send back
(other drives get to work). Thus drive cache ram that can burst quickly,
and generally small data transfers as well, will grow in benefit as you
add more scsi drives to a single cable. On the PCI bus end, it has to
operate at the bus speed, the question then is how well your specific
controller cooperates with other devices.

Now if you know for a fact that you are going to use scsi, and buy new
drives in the future, you might still want to get U160. I say this
because although controller cards are significantly more expensive, the
U160 drives of otherwise similar spec to uw or u2w are only a few
dollars different (and many of the lower end drives are going away).
Once you absorb the controller cost, drive expense by interface isn't
that different. And you will never find an uw 10k rpm or 15k rpm, they
will never be built.

D. Stimits, stimits at idcomm.com

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