🚀 go-pugleaf

James Bannon <jab@james-bannon.demon.co.uk> wrote in article
<iraAEKAV0Bl0EwWA@james-bannon.demon.co.uk>...
> Application. Is it a server or workstation? For servers, use SCSI
(preferably
> fast & wide or SCSI-III if you can get it); for workstations, use
Ultra-DMA EIDE
> as it's cheaper, unless you happen to be running applications demanding
higher
> bus bandwidths (e.g., Video direct to HD).


No,  UDMA EIDE drives provide sufficient bus bandwidth for video
applications including direct to HDs.  SCSI is the best choice for servers.


> 
> [The bit about sustained transfer rates is interesting. Consider SCSI-II:
The
> maximum theoretical transfer rate of such a device is 10 MB/sec (burst),
or
> roughly 4 MB/sec sustained, at least according to the official
specification.
> There is no way that SCSI-II could give 20 MB/sec sustained.]


Well, not quite.  Fast narrow SCSI2 has a peak burst of 10MB/sec. and can
sustain about 8.5MB/sec.  Fast wide peak burst of 20MB/sec. and sustained
about 17-18MB/sec.


> 
> For server-side applications, you have to be careful about how you attach
> devices to the bus. Mixing devices can cause the bus, whatever its
> specification, to run at the same speed as the slowest device. I would
consider
> having multiple controllers on the backplane with the fastest devices on
the
> same bus. This way, you spread the access load. This also applies
incidentally
> to certain hard drives, which brings me to my last point.
> 
> Now the Seagate Barracuda! This drive is designed to give sustained
throughput
> of 4 MB/sec; i.e., the fastest a SCSI-II bus can run.


No,  depending on which model Barracuda it'll sustain in the range of
5.5-11MB/sec.


> At that speed,
> interleaving reads/writes from applications with differing requirements
is going
> to be slower than EIDE, even when using a decent controller.


The Barracuda 4XL is as fast as any UDMA drive except possibly the Fireball
SE.


> The way to get
> around this is to install the drive on a separate controller and reserve
the
> Barracuda for applications it's designed for, specifically Video transfer
direct
> to HD. So you see, the Barracuda is not a good device for a
general-purpose
> workstation!


A Barracuda is a great drive for a workstation when connected to a
busmastering PCI controller;  it's just that it's very expensive compared
to a UDMA drive.

Regards,

Ron Reaugh