Re: [opensuse] eSATA and SuSE 9.3 -- UPDATE and a QUESTION

On Sun, Dec 28, 2008 at 11:39 AM, Robert Paulsen wrote:

On Sunday 28 December 2008 9:15 am, Greg Freemyer wrote:

...

On Sat, Dec 27, 2008 at 9:47 PM, Robert Paulsen wrote: <snip>

...

MY QUESTION:

The card is a 32-bit/33mhz PCI card (not PCI express) and claims to support 3.0Gbps. I thought that the PCI bus was not fast enough for 3.0Gbps and PCI express was required. Am I missing something? Am I simply wrong about the PCI bus' capabilities?

Bob

In reality there are 2 basic modes: Sata-1 and Sata-2. The most obvious difference is speed, but sata-2 offers some other features you might want to use.

For some reason, controller / disk manufacturers like to claim 3Gbs capability, when they really mean Sata-2 compatibility. ie. Not only "faster" but also other enhanced features.

As to speed on PCI, I think you are right. The only thing you really get is access to the other enhanced features. (ie. NCQ for one is only supported on SATA-2 drives.)

Also, a single sata drive can NOT saturate a 1.5Gbs connection, so more speed is not needed for point to point connections.

Sata has something called PMP. aiui, it is like a sata-hub. You connect one side to your controller and the other side to a number of different sata-drives. With PMPs in use the controller / hub connection can saturate a 1.5Gbs link, so you would want to use 3.0Gbs for that config.

I am confused by all of the above. Both the drive and that card claim 3Gbps. Are you saying that the drive really doesn't (can't?) xfer data at 3Gbps?

The drive can provide bursts of data a 3Gbps, but it cannot maintain it for any length of time. Not even if you do a pure sequential read or write. If the drive has a write cache, then you can fill the cache at 3Gbps, but you cannot get data to the actual platters that fast. I'll let you calculate how long it takes to fill a 16MB cache at 3Gbps, but not very long.

You say that I am right (presumably about PCI bus not supporting 3Gbps), but then seem to imply the PCI bus will support multiple drives that add up to over 1.5Gbps?

I should have said that even with PCI-express 3Gbps is wasted unless you have multiple drives hanging off of a single port via a PMP (hub/switch).

Sorry for being dense!

Bob

-- Greg Freemyer Litigation Triage Solutions Specialist http://www.linkedin.com/in/gregfreemyer First 99 Days Litigation White Paper - http://www.norcrossgroup.com/forms/whitepapers/99%20Days%20whitepaper.pdf The Norcross Group The Intersection of Evidence & Technology http://www.norcrossgroup.com -- To unsubscribe, e-mail: opensuse+unsubscribe@opensuse.org For additional commands, e-mail: opensuse+help@opensuse.org