4 ms·

This part is strange: "NVMe drive — an M.2 SSD looks almost identical, but has two notches instead of one. Generally an SSD will perform to the tune of hundreds

This part is strange: "NVMe drive — an M.2 SSD looks almost identical, but has two notches instead of one. Generally an SSD will perform to the tune of hundreds of MB/s instead of thousands." First, both are SSDs, so I don't know what he is trying to compare. Both use M.2, but different keys from the sounds of it (the "notches"). M.2 drives can be either SATA or NVME, but it is harder to come across a SATA M.2 drive than an NVME drive these days, so I'm having trouble seeing the point.

onli 6y ago
There are some M.2 SATA SSDs around that get regularly confused with NVMe SSDs. He for sure wanted to warn against SATA SSDs. Though for the Pi a SATA SSD would be fast enough.
- charwalker 6y ago
  And likely even a Pi4 couldn't take full advantage of an NVME drive except in specific workloads or setups. I'd use a SATA M.2 if needed to save 40% of the cost on the same size SSD. Or just a random thumb drive I have around. The Pi4 compute unit has a PCIe x1 slot, I think, and that could better put an NVME drive to use. But at that cost, for the drive and Pi, I don't see it being widely used outside of hobby or home use. I'm excited about this and how the official Pi4 firmware now supports USB boot. Maybe if you used the Pi to run a NAS and wanted the NVME drive as accelerated cache (it can do H.265, 4kp60 decode, and H.264)? But can a Pi even process an NVME drives bandwidth via it's CPU/etc or Gigabit Ethernet/USB 3.0/GPIO add on? Edit: This guide is basically 1. Put SSD in adapter and 2. Set up USB boot then clone SD card to SSD. How is this article not just a forum post like the dozens of others that provide the same information and process?
  - wtallis 6y ago
    > I'd use a SATA M.2 if needed to save 40% of the cost on the same size SSD. Or just a random thumb drive I have around. There are now lots of low-end M.2 NVMe SSDs on the market, and M.2 SATA SSDs are becoming uncommon. So there's no price remaining price advantage for M.2 SATA over M.2 NVMe—certainly not 40%—and it is not uncommon to find M.2 NVMe sale prices that are better than any M.2 SATA SSD price, since the more popular NVMe SSDs get better and more frequent discounts than the niche M.2 SATA SSDs. And the M.2 SSDs on the market with the lowest absolute cost (rather than per GB) are usually the Intel Optane Memory 16GB NVMe SSDs that were intended for use as cache devices, but have enough capacity for lots of embedded Linux use cases while also outperforming SATA SSDs of any capacity.
- jasonjayr 6y ago
  Often, most parts will just plain fail to fit, and fit exactly one way. But the keys for the different type of M.2 slots are not large enough on M.2 SATA vs M.2 SSD to prevent them from mixing up. It's easy to force, and forcing it will be fatal for the device. I know this from an expensive lesson I learned, long ago :(
  - wtallis 6y ago
    It's not quite that bad. A M.2 SATA SSD will fit into any socket designed for M.2 SATA or M.2 PCIe SSDs, without damage. A M.2 PCIe SSD that only uses two PCIe lanes will fit into any socket designed for M.2 SATA or M.2 PCIe SSDs, without damage. The only way to run into trouble is to force a M.2 PCIe SSD keyed for four lanes of PCIe into a M.2 socket keyed for SATA only with no PCIe lanes. Forcing this requires you to install the drive upside down and overcome the 0.5mm misalignment of the 1.2mm wide notch in the drive (meant to be filled by a 1.1mm key in the slot). If you merely install a SATA SSD in a slot only wired for PCIe, or a PCIe x2 SSD into a slot only wired for SATA, the drive will fail to work but nothing will be damaged. (You could theoretically also end up in trouble by forcing a SATA or PCIe x2 M.2 SSD into an appropriate slot, but upside down. However, this requires considerably more stupidity on the part of the user because in this scenario the SSD has two notches in the connector, so it is fairly obvious that any mechanical difficulty with installation could be due to having the card upside down. When installing a drive with only one notch, it's less obvious that the difficulty arises from a fundamental and intentional incompatibility.)
    - jasonjayr 6y ago
      (Whatever I did; it let out the magic smoke, and the M.2 device was visibly scorched. The 2nd time I ordered the same part and very carefully examined the keying did I realize my error...)
- ascagnel_ 6y ago
  For what it’s worth, unless you’re somehow able to dedicate a PCI-E lane to a USB port, the USB spec will be what limits you. I switched a Pi4 to boot from an older, spare USB SATA SSD a few weeks ago, and it’s reporting 1566MB/924MB on the same hdparm tests as the article (about a 10% drop-off).
  - davrosthedalek 6y ago
    SATA III is 600MB/s max. So either something is funky with the hdparm test (host side cache?) or it's not SATA.
    - ascagnel_ 6y ago
      The run uses a cache (hdparm -tT); I was more interested in relocating the results in the screenshot [0] than doing a more relevant test. [0] https://miro.medium.com/max/1400/1*xcGnOTsPvZtPdGSj8yODiA.png https://miro.medium.com/max/1400/1*xcGnOTsPvZtPdGSj8yODiA.pn...
deleted 6y ago
[deleted]

onli 6y ago

There are some M.2 SATA SSDs around that get regularly confused with NVMe SSDs. He for sure wanted to warn against SATA SSDs. Though for the Pi a SATA SSD would be fast enough.

charwalker 6y ago
And likely even a Pi4 couldn't take full advantage of an NVME drive except in specific workloads or setups. I'd use a SATA M.2 if needed to save 40% of the cost on the same size SSD. Or just a random thumb drive I have around. The Pi4 compute unit has a PCIe x1 slot, I think, and that could better put an NVME drive to use. But at that cost, for the drive and Pi, I don't see it being widely used outside of hobby or home use. I'm excited about this and how the official Pi4 firmware now supports USB boot. Maybe if you used the Pi to run a NAS and wanted the NVME drive as accelerated cache (it can do H.265, 4kp60 decode, and H.264)? But can a Pi even process an NVME drives bandwidth via it's CPU/etc or Gigabit Ethernet/USB 3.0/GPIO add on? Edit: This guide is basically 1. Put SSD in adapter and 2. Set up USB boot then clone SD card to SSD. How is this article not just a forum post like the dozens of others that provide the same information and process?
- wtallis 6y ago
  > I'd use a SATA M.2 if needed to save 40% of the cost on the same size SSD. Or just a random thumb drive I have around. There are now lots of low-end M.2 NVMe SSDs on the market, and M.2 SATA SSDs are becoming uncommon. So there's no price remaining price advantage for M.2 SATA over M.2 NVMe—certainly not 40%—and it is not uncommon to find M.2 NVMe sale prices that are better than any M.2 SATA SSD price, since the more popular NVMe SSDs get better and more frequent discounts than the niche M.2 SATA SSDs. And the M.2 SSDs on the market with the lowest absolute cost (rather than per GB) are usually the Intel Optane Memory 16GB NVMe SSDs that were intended for use as cache devices, but have enough capacity for lots of embedded Linux use cases while also outperforming SATA SSDs of any capacity.
jasonjayr 6y ago
Often, most parts will just plain fail to fit, and fit exactly one way. But the keys for the different type of M.2 slots are not large enough on M.2 SATA vs M.2 SSD to prevent them from mixing up. It's easy to force, and forcing it will be fatal for the device. I know this from an expensive lesson I learned, long ago :(
- wtallis 6y ago
  It's not quite that bad. A M.2 SATA SSD will fit into any socket designed for M.2 SATA or M.2 PCIe SSDs, without damage. A M.2 PCIe SSD that only uses two PCIe lanes will fit into any socket designed for M.2 SATA or M.2 PCIe SSDs, without damage. The only way to run into trouble is to force a M.2 PCIe SSD keyed for four lanes of PCIe into a M.2 socket keyed for SATA only with no PCIe lanes. Forcing this requires you to install the drive upside down and overcome the 0.5mm misalignment of the 1.2mm wide notch in the drive (meant to be filled by a 1.1mm key in the slot). If you merely install a SATA SSD in a slot only wired for PCIe, or a PCIe x2 SSD into a slot only wired for SATA, the drive will fail to work but nothing will be damaged. (You could theoretically also end up in trouble by forcing a SATA or PCIe x2 M.2 SSD into an appropriate slot, but upside down. However, this requires considerably more stupidity on the part of the user because in this scenario the SSD has two notches in the connector, so it is fairly obvious that any mechanical difficulty with installation could be due to having the card upside down. When installing a drive with only one notch, it's less obvious that the difficulty arises from a fundamental and intentional incompatibility.)
  - jasonjayr 6y ago
    (Whatever I did; it let out the magic smoke, and the M.2 device was visibly scorched. The 2nd time I ordered the same part and very carefully examined the keying did I realize my error...)
ascagnel_ 6y ago
For what it’s worth, unless you’re somehow able to dedicate a PCI-E lane to a USB port, the USB spec will be what limits you. I switched a Pi4 to boot from an older, spare USB SATA SSD a few weeks ago, and it’s reporting 1566MB/924MB on the same hdparm tests as the article (about a 10% drop-off).
- davrosthedalek 6y ago
  SATA III is 600MB/s max. So either something is funky with the hdparm test (host side cache?) or it's not SATA.
  - ascagnel_ 6y ago
    The run uses a cache (hdparm -tT); I was more interested in relocating the results in the screenshot [0] than doing a more relevant test. [0] https://miro.medium.com/max/1400/1*xcGnOTsPvZtPdGSj8yODiA.png https://miro.medium.com/max/1400/1*xcGnOTsPvZtPdGSj8yODiA.pn...

deleted 6y ago

[deleted]