Re: M.2 storage expansion for RPI 4 (and maybe other boards)

On Wed, 31 Jul 2024 13:39:48 +0100
Nuno Teixeira <eduardo@freebsd.org> wrote:

> Hello all,
> 
> From bsdnow I've read about a M.2 expansion board that I'm looking for.
> ( https://www.bsdnow.tv/569?utm_source=bsdweekly )
> 
> The board is https://geekworm.com/products/x862 that it is compatible with
> M.2 NGFF SATA SSDs only, not compatible with NVMe M.2 SSDs, so disk should
> be choosed carefully.

	M2 SATA is just SATA in a different package it is no faster than
any other SATA drive and seems to be on the way out. It was mostly about
making laptop drives smaller. I would avoid it IIWY.

	M2 NVME over PCI-e OTOH is capable of blisteringly fast speeds, the
PCI-e 3 ones serving my /home mirror hit nearly 3GB/s and they're
considered slow ones - fast ones claim over 7GB/s (yes bytes not bits).

> Currently using a USB3 external SSD disk, should I expect a great
> performance improvement?

	Probably not with M2-SATA - USB-3 is pretty quick. M2 NVME OTOH
will beat anything else by a very healthy margin. Things to watch for 

- PCI-e level and number of lanes needed - make sure the latter matches your
slots. The speed will be determined by the lowest PCI-e level and the
number of lanes. Most M2-NVME drives require four lanes.
- Four slot M2 NVME PCI-e x16 cards usually require a sixteen lane slot with
bifurcation support to four sets of four lanes. The ones that don't cram
everything down four lanes.
- Some M2 slots on motherboards are only single lane - it seems strange to
think of 7-800MB/s as slow but that's how it struck me when I met one.

-- 
Steve O'Hara-Smith <steve@sohara.org>