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
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