Re: [Avid-L2] Disk Speed limited to 300 Mbs on dock that supports Sata III?

John, you use the terms MB/s and Mb/s interchangeably.  They are not the same thing!

Jeff Kreines

Kinetta

jeff@kinetta.com

kinetta.com

Sent from iPhone. 

On Nov 26, 2020, at 11:31 AM, Marcel B. <bncrcaxlr@gmail.com> wrote:

 Hi,
All I can contribute to this discussion is my experience with USB 3.1 gen 1, 3.1 gen 2.

My CalDigit dock provides USB 3.1 gen 1 and 3.1 gen 2. Using PNY SSD 6GB/s on a USB 3.1 gen 2 Startech Toaster I get around 325 MB/s with gen 1 and 490 with gen 2.

Marcel

On 26/11/2020 12:12, pale.edit@gmail.com wrote:

I'd definitely put more stock in what Dom (Gowanus Canal) says, he's way more knowledgeable than me, but I did notice a speed boost with the same hardware when I switched to a PCI 3 PC from a PCI 2 Mac Pro 2010 recently.  There are lots of factors involved. 

On Thu, Nov 26, 2020 at 10:10 AM John Moore <bigfish@pacbell.net> wrote:

I was thinking that but thought I was bypassing that by going through the expansion chassis.  Now you point out what I hadn't considered.  The expansion chassis is connected through the MacPro PCI 2.0 16 lane slot so I thought it would have tons of bandwidth potential but I hadn't thought about if my expansion chassis being PCI 2.0.  Even though the backplane has 16 lanes the Allegro USB 3 card is probably sitting in a PCI 2.0 slot.

Here's specs I found:

Summary of PCI Express Interface Parameters:

Data Rate: PCIe 3.0 = 1000MB/s, PCIe 2.0 = 500MB/s, PCIe 1.1 = 250MB/s. Total Bandwidth: (x16 link): PCIe 3.0 = 32GB/s, PCIe 2.0 = 16GB/s, PCIe 1.1 = 8GB/s.

From this it looks like with the 16 lane and 2.0 I should have 16GB/sec and PCIe 2.0 is 500MB/sec.  So it would seem the food chain feeding up to the dock should handle at least something closer to 500 MB/sec.  From this it still  makes me think the dock itself may support 6G but could be built with SATA II chipset.  Given I got it off the shelf at Fry's I wouldn't be surprised.  The spec said it supports 6G but does that really mean it has 6G technology components or is it just limiting a 6G drive to 3G SATA II?

On Wed, Nov 25, 2020 at 08:37 PM, <pale.edit@gmail.com> wrote:

I think you are maxing out the PCI 2.0 slots in the old Mac Pro.   In a PCI 3.0 system you will get better performance.

On Wed, Nov 25, 2020 at 11:17 PM John Moore <bigfish@pacbell.net> wrote:

I've got a pair of Seagate IronWolf SSDs that are Sata III and spec says they can get approx 550 Mbps in Sata III.  The dock(s) are connected to a Sonnet Allegro PCIe card with 4 USB 3.0 connections.  I can only seem to get around 300 MB/sec per individual drive but when I raid 0 them I still only get around 300 MB/sec.  I had thought given the vintage of my docks they were all SATA II.  I went to Fry's and got the dual dock because it said it supports 1.5, 3.0 & 6.0G Sata drives.  I took that to mean it the dock slots are 6G Sata III.  When I test the individual slots on the dual dock I only get the 300MB/sec.  This leads me to believe that the dock is only Sata II slots.  Even given that if I raid 0 the two slots I still only get just a little over 300 MB/sec.  I figured it wouldn't double but may get 1.5 times the individual drive speed.  I then split the drive set across two docks both USB 3 to the Sonnet Allegro card.  I get a little better like 333 Mbps.  The Allegro is in my cyclone microsystems expansion chassis hooked up to my mid 2012 MacPro using the 16 lane slot to connect the two.  I know the MacPro is Sata II in the tower but I would have thought if the dual dock is truly 6G Sata III then I should be able to get close to 550 Mbps for an individual SSD . 

 

So what in the food chain is limiting things to around 300 Mbps regardless of whether I raid or not.  The conversion of USB 3 5 Gbps to Mega Bytes per second is 625MB/sec.  So in theory I should be able to get close to the IronWolf spec of 550 MB/sec shouldn't I.  I know there is only one controller in the Allegro card I have.  I've ordered another to get more USB 3 connections and the new one is the dual controller version.  Maybe when I get that in I'll see if splitting across two USB 3 cards helps.  Am I missing some overall architecture limitation under the hood?  I know sometimes I think in theoretical terms without the experience of practical application.

 

Someone please bit slap me into a better understanding of what's going on.  ;-)

 

John Moore Barking Trout Productions Studio City, CA bigfish@pacbell.net