TR Forums

I'm trying to find an external PCIe card enclosure that connects to laptops via Thunderbolt 3, that will provide me with at least 8 PCIe lanes (2.0 or 3.0). I want to buy a video capture card that uses PCIe 8x 2.0, but none of the ones I've found so far offer more than 4 lanes of connectivity

Thank you for any suggestions!

internetsandman wrote:

I'm trying to find an external PCIe card enclosure that connects to laptops via Thunderbolt 3, that will provide me with at least 8 PCIe lanes (2.0 or 3.0). I want to buy a video capture card that uses PCIe 8x 2.0, but none of the ones I've found so far offer more than 4 lanes of connectivity

As a guess, that's likely due to the design of Intel's Thunderbolt 3 controllers, which use a PCIe 3.0 x2 or x4 link internally. Furthermore, 8 lanes of PCIe 3.0 exceeds the bandwidth of a Thunderbolt 3 link by a fair bit, so I doubt anyone would bother trying to produce such a device.

Does the card function with 4 lanes of throughput? Because that's all that's going to be available for a while yet.
IIRC 8 lanes of 2.0 should effectively be the same thing as 4 lanes of 3.0 in any case.

Vhalidictes wrote:

Does the card function with 4 lanes of throughput? Because that's all that's going to be available for a while yet.
IIRC 8 lanes of 2.0 should effectively be the same thing as 4 lanes of 3.0 in any case.

That's the thing, I don't know if the card will function properly. It's a Blackmagic Decklink Quad 2. I would get the Decklink Duo 2 (with a PCIe 4x 2.0 interface) but it's legitimately one less video input than I need. I've looked on a couple manufacturers websites (Sonnet and Akitio) and Sonnet has the Quad 2 listed as compatible with their Thunderbolt 3 expansion chassis, but I've heard elsewhere that it won't function properly.

I honestly don't know how PCIe 3.0 works when given a PCIe 2.0 device with more lanes than the 3.0 slot is wired for (even though theoretical bandwidth is the same IIRC)

internetsandman wrote:

Vhalidictes wrote:

Does the card function with 4 lanes of throughput? Because that's all that's going to be available for a while yet.
IIRC 8 lanes of 2.0 should effectively be the same thing as 4 lanes of 3.0 in any case.

That's the thing, I don't know if the card will function properly. It's a Blackmagic Decklink Quad 2. I would get the Decklink Duo 2 (with a PCIe 4x 2.0 interface) but it's legitimately one less video input than I need. I've looked on a couple manufacturers websites (Sonnet and Akitio) and Sonnet has the Quad 2 listed as compatible with their Thunderbolt 3 expansion chassis, but I've heard elsewhere that it won't function properly.

I honestly don't know how PCIe 3.0 works when given a PCIe 2.0 device with more lanes than the 3.0 slot is wired for (even though theoretical bandwidth is the same IIRC)

The extra lanes aren't physically connected, so there's no way to utilize that bandwidth. At best, the card's interface will operate at half speed.

internetsandman wrote:

Vhalidictes wrote:

Does the card function with 4 lanes of throughput? Because that's all that's going to be available for a while yet.
IIRC 8 lanes of 2.0 should effectively be the same thing as 4 lanes of 3.0 in any case.

That's the thing, I don't know if the card will function properly. It's a Blackmagic Decklink Quad 2. I would get the Decklink Duo 2 (with a PCIe 4x 2.0 interface) but it's legitimately one less video input than I need. I've looked on a couple manufacturers websites (Sonnet and Akitio) and Sonnet has the Quad 2 listed as compatible with their Thunderbolt 3 expansion chassis, but I've heard elsewhere that it won't function properly.

I honestly don't know how PCIe 3.0 works when given a PCIe 2.0 device with more lanes than the 3.0 slot is wired for (even though theoretical bandwidth is the same IIRC)

Would the Ultra Studio 4K Extreme 3 work for your needs? It is native Thunderbolt 3 so you wouldn't have to deal with an external GPU chassis.

the wrote:

internetsandman wrote:

Vhalidictes wrote:

Does the card function with 4 lanes of throughput? Because that's all that's going to be available for a while yet.
IIRC 8 lanes of 2.0 should effectively be the same thing as 4 lanes of 3.0 in any case.

That's the thing, I don't know if the card will function properly. It's a Blackmagic Decklink Quad 2. I would get the Decklink Duo 2 (with a PCIe 4x 2.0 interface) but it's legitimately one less video input than I need. I've looked on a couple manufacturers websites (Sonnet and Akitio) and Sonnet has the Quad 2 listed as compatible with their Thunderbolt 3 expansion chassis, but I've heard elsewhere that it won't function properly.

I honestly don't know how PCIe 3.0 works when given a PCIe 2.0 device with more lanes than the 3.0 slot is wired for (even though theoretical bandwidth is the same IIRC)

Would the Ultra Studio 4K Extreme 3 work for your needs? It is native Thunderbolt 3 so you wouldn't have to deal with an external GPU chassis.

Currently that would be massively overkill for my needs. I need my solution to be portable enough to fit in an oversized backpack with lots of other gear, and I need at least 5 3G SDI inputs for the productions I'm aiming to make. The Decklink Quad 2 fits in my budget, though barely, and allows me room to expand in the future. I just can't find an external chassis that can support it

If it isn't too forward, just what is your need? It may be that there is a better solution that is not being considered. Regardless, there just isn't any good solution for external pci-e x8. That is just a ton of bandwidth. 4 GB/S. PCI-e 2.0 8x is possible as it carries 5 GB/s, but PCI-e 3.0 is just not going to happen at nearly 8 GB/s.

Here is an option, but it isn't great for portability:
https://www.bhphotovideo.com/c/product/1303819-REG/akitio_ak_node_t3ia_aktu_thunderbolt3_external_pcie_box.html

internetsandman wrote:

the wrote:

internetsandman wrote:

That's the thing, I don't know if the card will function properly. It's a Blackmagic Decklink Quad 2. I would get the Decklink Duo 2 (with a PCIe 4x 2.0 interface) but it's legitimately one less video input than I need. I've looked on a couple manufacturers websites (Sonnet and Akitio) and Sonnet has the Quad 2 listed as compatible with their Thunderbolt 3 expansion chassis, but I've heard elsewhere that it won't function properly.

I honestly don't know how PCIe 3.0 works when given a PCIe 2.0 device with more lanes than the 3.0 slot is wired for (even though theoretical bandwidth is the same IIRC)

Would the Ultra Studio 4K Extreme 3 work for your needs? It is native Thunderbolt 3 so you wouldn't have to deal with an external GPU chassis.

Currently that would be massively overkill for my needs. I need my solution to be portable enough to fit in an oversized backpack with lots of other gear, and I need at least 5 3G SDI inputs for the productions I'm aiming to make. The Decklink Quad 2 fits in my budget, though barely, and allows me room to expand in the future. I just can't find an external chassis that can support it

The Ultra Studio 4K TB2 would fit your needs and be closer to your budget (assuming you don't already have the Decklink Quad 2). You'd need Apple's TB3 to TB2 adapter for it to work with a newer TB3 based system. Those two parts should be cheaper than the Decklink Quad 2 plus external TB3 based PCIe chassis. The other bonus is that by raw volume, this is smaller than some of the TB3 external enclosures.

To answer your question about external GPU interfaces, a 16x and 8x PCIe expansion card will work in a slot with only 4x lanes electrically wired to it. The catch is that PCIe 3.0 will demote itself to PCIe 2.0 speeds at the request of the expansion card. So dropping an 8x PCIe 2.0 card into an electrically wired 4x PCIe 3.0 slot will ultimately work at 4x PCIe 2.0 speeds, or half the bandwidth of the expansion card. There are PCIe bridge chips that will adapter 4x PCIe 3.0 into 8x PCIe 2.0 but I have yet to see one of these chips placed into an external Thunderbolt enclosed (TB2 or TB3). So conceptually it is possible but I am unaware of any actually on the market.

I think I may have found my solution and it was sort of sitting under my nose the whole time I've been shopping around

http://www.sonnettech.com/product/echoexpressse3.html

They say this box has two 8x electrical and one 4x electrical slots, which (if everything works) would not only give me the bandwidth I need upfront with the Decklink Quad, but also even more expansion room with other cards if need be

That's still less than the bandwidth of a native PCIe 2.0 x8 slot. Hopefully that doesn't cause issues.

just brew it! wrote:

That's still less than the bandwidth of a native PCIe 2.0 x8 slot. Hopefully that doesn't cause issues.

Doesn't a native PCIe 2.0 8x slot have ~40gbps bandwidth? The same as the 3.0 4x lanes afforded by Thunderbolt 3? From my limited knowledge, as long as I can access all 8 PCIe 2.0 lanes, I should be able to run the card at full bandwidth, maybe with a bit of latency from the bridge chips that are likely involved but I can't see that being too big a problem, though if I'm wrong I'd like to know sooner rather than later. Realistically speaking I don't even need "full bandwidth", I just need the Decklink Quad 2 to not be cut down to half speed

The page you linked says it has 2750 MB/s of bandwidth, so for some reason it is not utilizing the full 40 Gbps. I suppose it is possible that it is a typo.

just brew it! wrote:

The page you linked says it has 2750 MB/s of bandwidth, so for some reason it is not utilizing the full 40 Gbps. I suppose it is possible that it is a typo.

I emailed Sonnet Support, they told me it wasn't a typo and that TB3 reserves some bandwidth for video. This is the first I'm hearing about this, I thought it was simply PCIe that could be told to carry video or whatever else you needed

internetsandman wrote:

just brew it! wrote:

That's still less than the bandwidth of a native PCIe 2.0 x8 slot. Hopefully that doesn't cause issues.

Doesn't a native PCIe 2.0 8x slot have ~40gbps bandwidth? The same as the 3.0 4x lanes afforded by Thunderbolt 3? From my limited knowledge, as long as I can access all 8 PCIe 2.0 lanes, I should be able to run the card at full bandwidth, maybe with a bit of latency from the bridge chips that are likely involved but I can't see that being too big a problem, though if I'm wrong I'd like to know sooner rather than later. Realistically speaking I don't even need "full bandwidth", I just need the Decklink Quad 2 to not be cut down to half speed

No, it does not work that way and afaik none of the chassis even have bridge chips or switches, only some overpriced motherboards use them. The company that makes them was recently bought up and prices raised, it is rather lame.

A 2.0 x8 card in any TB3 chassis (at best x4 electrical regardless of physical slots) will run at 2.0 x4 at best, sometimes even x2 depending on the laptop/cable/chassis/firmware.

Without a complicated pci-e bridge chip (which may not even exist) always take the least number of real lanes and lowest generation of pci-e in the device chain when calculating available bandwidth.

FWIW 2.0 x4 is still a lot of bandwidth, your use case might have no issues. If you really need more its probably time to build a portable desktop or similar, lots of choices for ITX today. I do remember a MSI laptop from the haswell era with custom x16 3.0 dock, basically a giant riser board.

PS, of any current or announced gpu chassis, I would get the sonnet. Even though akitio and others are very similar price/features/chipset it has been Blessed By Apple™, so support and resale will likely be the best for awhile. It also is one of the few with a meaningful amount of working power delivery, 60W from apple version and 87W when they ship the 550w model.

The akitio was the first TB3 box that wasn't overpriced and/or had stupid technical problems but it is just too damn big. They have supported it well though. I mostly blame intel for its inane BS policy of not allowing board-only designs to be sold, otherwise there would be awesome DIY options with ITX cases.

Bauxite wrote:

internetsandman wrote:

just brew it! wrote:

That's still less than the bandwidth of a native PCIe 2.0 x8 slot. Hopefully that doesn't cause issues.

Doesn't a native PCIe 2.0 8x slot have ~40gbps bandwidth? The same as the 3.0 4x lanes afforded by Thunderbolt 3? From my limited knowledge, as long as I can access all 8 PCIe 2.0 lanes, I should be able to run the card at full bandwidth, maybe with a bit of latency from the bridge chips that are likely involved but I can't see that being too big a problem, though if I'm wrong I'd like to know sooner rather than later. Realistically speaking I don't even need "full bandwidth", I just need the Decklink Quad 2 to not be cut down to half speed

No, it does not work that way and afaik none of the chassis even have bridge chips or switches, only some overpriced motherboards use them. The company that makes them was recently bought up and prices raised, it is rather lame.

A 2.0 x8 card in any TB3 chassis (at best x4 electrical regardless of physical slots) will run at 2.0 x4 at best, sometimes even x2 depending on the laptop/cable/chassis/firmware.

Without a complicated pci-e bridge chip (which may not even exist) always take the least number of real lanes and lowest generation of pci-e in the device chain when calculating available bandwidth.

FWIW 2.0 x4 is still a lot of bandwidth, your use case might have no issues. If you really need more its probably time to build a portable desktop or similar, lots of choices for ITX today. I do remember a MSI laptop from the haswell era with custom x16 3.0 dock, basically a giant riser board.

The chassis I'm looking at (echo express SE III)has 2 8x electrical slots and 1 4x electrical (8x physical) slot listed in its spec sheet. I'm assuming it uses several bridge chips to achieve that

My use case involves a PCIe 2.0 8x card, which would be reduced to 4x in most chassis I've seen, and in the future I'm fairly certain I'll be using more bandwidth through that card than PCIe 2.0 4x can support (it would be a minimum of five downstream 1080p60 video feeds, and up to two upstream 1080p60 feeds)

That's why I'm very interested in the Echo Express SE III, but as JBI pointed out, the 2750MBps listed on the spec sheet is quite confusing

The Sonnet Echo Express III looks to be using the effective link speed converted to bytes with overhead removed. It is a very odd way of doing this as that figure is far from guaranteed due to other devices on the chain and if DP is encapsulated alongside PCIe.

the wrote:

The Sonnet Echo Express III looks to be using the effective link speed converted to bytes with overhead removed. It is a very odd way of doing this as that figure is far from guaranteed due to other devices on the chain and if DP is encapsulated alongside PCIe.

Assuming that it's the only device in the chain (one echo express with one expansion card) would I be able to trust that I could get the full bandwidth out of it? Or would I be better off to keep looking?