Re: SATA Cards: How is their actual bandwith calculated?

Happy New Year to all and many thanks for your responses .

It has started making sense now, but:

They have an entry level "Tempo Serial ATA" card

This card only has a 32-bit PCI interface. In your PowerMac G4, the PCI
bus runs at 33 MHz. A 32-bit card is therefore limited to 4 * 33 = 132
MB/s maximum data throughput.

That is very-very interesting. Could you please explain to me why you
used the number 4?

I currently have a Tempo Trio [http://www.sonnettech.com/product/
tempo_trio.html] and a Tempo ATA133 on two of my G4s and both of them
are set up to RAID 0, using the OS X soft raid and with 2 ATA drives
connected to each of the separate channels.

A card like the Sonnet Tempo 133 would theoretically give 133MB/s per
channel right? But the 32-bit 33 Mhz bus can only provide 132MB/s.
Isn't this slightly absurd on behalf of the card manufacturing
companies to advertise such a feat when is not actually true in real
life?

Consider the Tempo SATA X4i by comparison:

<http://www.sonnettech.com/product/tempo_sata_x4i.html>

This has a 64-bit PCI bus interface, so in your G4 it would have a
theoretical limit of 260 MB/s. This card definitely says it has 3 GB/s
maximum per port, so there is no question it will be able to saturate
your PCI bus and get maximum performance out of all connected drives
(given the limits of your computer).

Could you please explain what's the math behind the 260MB/s rate?

In your PowerMac G4, the PCI bus is also used by the secondary ATA/66
controller, the EIDE bus (CD/DVD), audio circuitry and built-in USB. If
you are using any of those (or any other PCI cards), then something is
going to suffer limited throughput if you try to saturate your PCI bus.

Invaluable information. Thanks.

Note the potential conflict with other PCI cards, ATA/66, EIDE, USB and
audio.

Are there any known figures when the audio or usb bus are being used?
Should i assume that by disabling the sound outputs from the control
panel would free up some bandwidth?

To get better performance than that, you would have to upgrade to a
PowerMac G5 or Mac Pro.

David, that is my wish as well. But the cost of upgrading the whole of
my A/V system would super-exceed my current purchasing capability.
Plus Santa did not fill my Apple Mac sock this year. Would that imply
that mean i have been a bad?

With a single drive, you would only achieve this speed with data to/from
the drive's RAM cache, so the peak or burst rate is significant. The
sustained rate (for transfer to/from the drive platters) will be
considerably lower. It might get up to something like 120 MB/s for very
fast drives, but only in some parts of the drive. Most of it is likely
to be considerably slower.

What would be the average speed of a 7200rpm SATA drive? For a
10,000rpm perhaps?
And should i simply multiply by 2, if i have a two drives in a RAID 0
to calculate the throughput?

Back to my current setup with the Sonnet Tempo 133;

Am i really achieving any higher HD speeds with the OS X RAID 0
feature and two separate drives on each of the card's channels?

Would it make any difference if i had four drives connected instead
(again in RAID 0)?

And come to think about it, what you would think is the average read/
write speed of a fairly good ATA 100 drive?

And i think i am left to suppose that when i am using the Sonnet Tempo
Trio card then the two ATA 133 channels, the two USB ports and the
two Firewire ports that are all located on the card, are all sharing
that 132MB/s throughput. Wrong/ false?

Last but not least, would anyone tell how much the OS X raid taxes the
CPU?

Many thanks to all and sorry for this last string of questions.
.

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