HSA PCIe Lanes

[_tempted_]

I’ve been wanting to build a cheap NAS system. I’d like to use an Icy Dock mobile rack that houses several 2.5 in drives in a single 5.25 bay. So I’m also looking at cheap $10 LSI cards on eBay which I know have their limitations but I’m ok with them (2GB max size per drive and SATA II speeds). The question I’ve got is about PCIe lanes. The description about the cards say 8x so if I need two of them it would be best to find a system with 2 8x or 16x PCIe slots. Is that correct? If it matters I would probably use TrueNAS.

 

https://docs.broadcom.com/doc/12352186
 

Older system with two 16x PCIe slots

https://www.dell.com/downloads/global/products/precn/en/precn_t3400_specsheet.pdf

 

Example IcyDock cage:

https://www.ebay.com/itm/ICY-DOCK-Expresscage-MB326SP-B-6-bay-2-5-HDD-SDD-5-25-cage-/284151247575?_trksid=p2349624.m46890.l49292
 

[Jae Tee]

Remember that many mobo with multiple 16x slots actually only pin them for 8x anyway. However I've never seen an 8x or smaller being less than fully pinned. So it seams like you'll be fine either way.

[_tempted_]

8 hours ago, Jae Tee said:

Remember that many mobo with multiple 16x slots actually only pin them for 8x anyway. However I've never seen an 8x or smaller being less than fully pinned. So it serves like you'll be fine either way.

@Jae Tee I’ve been mindful of that. I see Dell Optiplex for sale but usually have only one 16x and the next highest bandwidth port has 4x. In the tech docs I have seen it stated “8x wired as 4x”. Dell Precision 3400+ seems to consistently have two PCIe slots that are at least 8x. Thanks.

[Nick7]

You can also look for older systems with x79 motherboards. There you can get sandy/ivy bridge generation of CPU's for quite cheap, and they have 40 PCIe lanes.

It's an option..

[mariushm]

While the controller boards are pci-e x8 or pci-e x16, they will also run in pci-e x4 or even pci-e x1 slots.

PCI-e is designed like that, to be flexible, and allow mismatch between the number of actual lanes in the slot and the lanes in the edge connector of a card.

There are even motherboards which have pci-e x1 and x4 slots that don't have a wall at the end of the connector, so that you can plug a pci-e x4 in the pci-e x1 slot, or a pci-e x8 in the pci-e x4 slot , as long as there's nothing obstructing the path of the edge connector - part of the edge connector of the card can simply stay in air and won't bother anyone.

 

Alternatively, you can literally CUT the edge connector of the card carefully to bring it down to pci-e x4 or even pci-e x1. At 10-20$, it's not like you're gonna miss much if you cut too much accidentally.

See videos below, but note you don't need a high speed drill or fancy tools - you can get an exacto knife / sharp blade and repeatedly make a cut across the undesired contacts until you get half in or 2/3 rds in and then you can get some pliers to bend and break off the edge connector side you don't need. Then use some nail file or sandpaper (or whatever is called) or something to finish the end of the connector to be able to get the card in the slot.

 

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The cards being so old will most likely be only pci-e 2.0, so that means a maximum of 500 MB/s per lane. Even with 4 lanes, you still have 2 GB/s ... realistically around 1.8 GB/s - with mechanical hard drives it's not gonna be an issue ... you have 200-300 MB/s max with a mechanical drive. Even with raid, you won't get close to 2 GB/s

 

You'd probably gonna be fine even with a pci-e x1 card (or card cut down to x1 - though keep in mind some cards have firmware which refuses to run at x1, but they'll run at x4 or x8) ... even reading/writing to 2 drives at same time, you're probably not gonna saturate that 500 MB/s.

 

If you don't feel like cutting, there's pci-e riser cables which change a pci-e x4 to a pci-e x16, or a pci-e x4 to pci-e x4 but without the wall at the end, so you can plug your pci-e x8 or x16 card.

They work especially well if you buy a low profile version of a controller, as such cards will sit a few cm above the board if you screw them to the case with the low profile bracket ... and that's the right height to have a riser cable/adapter between the motherboard and your card

 

Example cables / adapters :

 

pci-e x4 to pci-e x4 WITHOUT wall at the end : https://www.amazon.com/ADT-Link-Extension-Extender-Conversion-Vertical/dp/B07THWKR68/

 

pci-e x1 to pci-e x1 WITHOUT wall at end: https://www.amazon.com/Express-Extender-Extension-Gold-Plated-Connector/dp/B07J2BJPDN/

 

pci-e x4 to x16 riser cable : https://www.amazon.com/Express-Female-Riser-Mining-Cable/dp/B00CJE0KJ6/