Re: [gentoo-user] m.2 nvme stick not what I was expecting at all.

[Michael <confabulate@kintzios.com>]

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On Wednesday, 26 February 2025 14:43:41 Greenwich Mean Time Dale wrote:
> Rich Freeman wrote:
> > On Tue, Feb 25, 2025 at 12:26 PM Dale <rdalek1967@gmail.com> wrote:
> >> I'm pretty sure you mentioned this once before in one of my older
> >> threads.  I can't find it tho.  I use PCIe x1 cards to connect my SATA
> >> drives for my video collection and such.  You mentioned once what the
> >> bandwidth was for that setup and how many drives it would take to pretty
> >> much max it out.  Right now, I have one card for two sets of LVs.  One
> >> LV has four drives and the other has three.  What would be the limiting
> >> factor on that, the drives, the PCIe bus or something else?
> > 
> > It depends on the PCIe revision, and of course whether the controller
> > actually maxes it out.
> > 
> > 1x PCIe v3 can do 0.985GB/s total.  That's about 5 HDDs if they're
> > running sequentially, and again assumes that your controller can
> > actually handle all that data.  For each generation of PCIe
> > forward/backwards either double/halve the transfer rate.  The
> > interface works at the version of PCIe supported by both the
> > motherboard+CPU and the adapter card.
> > 
> > If you're talking about HDDs in practice the HDDs are probably still
> > the bottleneck.  If these were SATA SSDs then odds are that the PCIe
> > lane is limiting things, because I doubt this is an all-v5 setup.
> > 
> > https://en.wikipedia.org/wiki/PCI_Express#History_and_revisions
> > 
> > The big advantage of NVMe isn't so much the bandwidth as the IOPS,
> > though both benefit.  Those run at full PCIe 4x interface speed per
> > drive, but of course you need 4 lanes per drive for this, which is
> > hard to obtain on consumer motherboards at any scale.
> 
> This I think is what I needed.  As it is, I'm most likely not maxing
> anything out, yet.  The drives for Data, torrent stuff, stays pretty
> busy.  Mostly reading.  My other set of drives, videos, isn't to busy
> most of the time.  A few MBs/sec or something, playing videos type
> reading.  Still, next time I power down, I may stick that second card in
> and divide things up a bit.  Might benefit if those cards aren't to great. 
> 
> I did copy this info and stuck in in a text file so I don't have to dig
> for it again, or ask again.  ;-) 
> 
> Thanks.
> 
> Dale
> 
> :-)  :-) 

The other thing to straighten out, already hinted at by Rich et al., is an 
NVMe M.2 card in a USB 3 enclosure won't be able to maximise its SSD transfer 
rates.  To do this it will require a Thunderbolt connector and a corresponding 
Thenderbolt PC port, which will connect it internally to the computer's PCIe 
bus, rather than USB/SATA.  Hence a previous comment questioning the perceived 
value of paying for a NVMe SSD M.2 form factor within a USB enclosure.  It 
won't really derive much if any performance benefit compared to a *good* 
quality USB 3 flash drive (UFD), which can be sourced at a much lower price 
point.

External storage medium, transfer protocol, device controller, PC bus and 
cables/connectors/ports, will all have to have aligned generations of 
technology and standards, if you expect to make most of their advertised 
transfer speeds.  Otherwise you'll be stuck at some component of a lower 
performance providing a bottleneck to your aspirations.  ;-)

Sometime ago I bought a SanDisk 1TB Extreme Portable SSD, which has a USB-C 
connector and a USB 3.2 Gen 2 controller as a replacement for a flaky USB 3.0 
stick.  It is slightly bigger than a small UFD and more expensive than the 
cheaper UFD offerings, but the faster speeds more than compensate for it.  At 
the time I bought it, external NVMe M.2 drives were too expensive and I only 
had USB 3.0 ports anyway.  So in my use case it was offering the best bang for 
my buck.

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