Comment by erosenbe0
4 years ago
Most likely not valid.
What was the external enclosure?
You need an ATX 3.3V rail that has a 15ms hold up time and whatever other sequencing these devices were designed for.
The buck converter in a USB enclosure isn't going to cut it for a valid test.
Could you explain the question?
As far as I understand (which is little more than this twitter thread) the flush command should only return a success response once any data has been written to non-volatile storage.
If the storage still requires power after that point to maintain the data, that storage area is volatile, no?
So if the device has returned success (and I'm not going to claim that they've ensured that it was the device returning success and not the adapter, or that they even verified what the response was - those seem like valid questions) presumably the power wind-down should not be an issue?
That said, I presumed by "disconnect the cable" the test involved some extension cable from the motherboard straight to drive to make it easier to disconnect - would that therefore make it a valid test of the NVMe?
You understand incorrectly. Flush means data is in volatile DRAM in the device. That's how SSDs work.
Extension cable from motherboard would certainly make it invalid. These devices are not hot swap and may expect power hold up and sequencing from the supply.
You're wrong. Please read the NVMe spec, section 7.1:
> the Flush command shall commit data and metadata associated with the specified namespace(s) to non-volatile media
It has nothing to do with DRAM. The spec is explicit about what Flush does. The drive is not allowed to ack the flush until the data and drive metadata are on durable storage.
For a discussion on what happens when the drive has power loss protection, see 5.24.2.1 - in that case the write cache (aka DRAM) is considered non-volatile and Flush can be a no-op. None of the drives I tested fell into that category however.
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