Re: SCSI or IDE
On Sun, 24 Nov 2002 22:13, Vector wrote:
> > > You can put a lot more disks on a single SCSI
> > > controler, than on a IDE controler, and there (afaik, i could be
> > > mistaken) two drives on one bus cannot work simultaneously and share
> > > the bandwidth (which isn't a problem with SCSI, if you have 160 MB/s
> > > bus, and 3 disks that can make about 40MB/s, you can have all 120MB/s)
> >
> > 3ware IDE controllers support up to 12 drives. You won't find many SCSI
> > controllers that can do that and deliver acceptable performance (you
> > won't get good performance unless you have 64bit 66MHz PCI).
>
> That is not true.
What are you claiming is not true?
> Ultra2 can't do 160MB/s. Ultra2 is limited to 80MB/s. U160 (or ultra3)
> can do 160MB/s. And perhaps, yes, Ultra2 vs ATA-133 might be comparable.
> And U320 is now and can do 320MB/s....such is and has been the evolution of
> both standards.
ATA-133 for two disks (or one disks for 3ware type devices) is more than
adequate. U160 for more than 4 disks will be a bottleneck.
> > 3) SCSI termination.
>
> Huh? I'd honestly have to say this falls into the same category as 1)
> Incompetant administrators. Get the termination right and it all works
> just fine, which is now easier than ever since controllers have been able
Unfortunately the administrators don't always get a chance to inspect the
hardware or fiddle with it.
I often don't get to touch the hardware I administer until after it has been
proven to be broken.
Sun likes to do all the hardware maintenance (it's quite profitable for them).
Sun employees often aren't able to terminate SCSI properly.
For these and other reasons a company I am working for is abandoning Sun and
moving to Debian on PC servers.
> to autoterminate for many many years and now they are building terminators
> right into the cable. And there are other factors like cable quality and
> length. It's cerntaily more complicated but again, I feel it's worth it
> once you know what you are doing.
Regardless of auto-termination and terminators built into cables, if you
install the wrong parts then you can still stuff it up.
When you've had a repair-man from the vendor use a hammer to install a CPU you
learn to accept that any hardware can be broken no matter how well it's
installed.
> > SCSI drives tend to have higher rotational speeds than IDE drives and
> > thus
>
> True, and in your first reply on this thread didn't you quote this as one
> of the primary factors determining speed?
Yes. However for bulk IO it's rotational speed multiplied by the number of
sectors per track. A 5400rpm IDE disk with capacity 160G will probably
perform better for bulk IO than a 10,000rpm SCSI disk with capacity 36G for
this reason.
A high rotational speed helps seek times a lot too, but a big cache and a
battery-backed write-back cache can make up for this (admittedly this isn't
something you'll see in a typical IDE-RAID solution).
> Hmm, yeah, there's crap in both sectors that's for sure. I can't say I've
> been a huge fan of IBM drives in the past.
IBM drives used to be really good. They used to run cool, quietly, and
reliably. I've had IBM drives keep working in situations where other brand
drives failed from heat.
It seems that whenever a vendor gets a reputation for high quality they then
increase the volume, sub-contract the manufacturing to a country where they
can pay the workers $0.10 per hour, and the results are what you would
expect. :(
--
http://www.coker.com.au/selinux/ My NSA Security Enhanced Linux packages
http://www.coker.com.au/bonnie++/ Bonnie++ hard drive benchmark
http://www.coker.com.au/postal/ Postal SMTP/POP benchmark
http://www.coker.com.au/~russell/ My home page
Reply to: