Atomic writes without tears

Posted Jun 3, 2024 18:02 UTC (Mon) by andresfreund (subscriber, #69562)
Parent article: Atomic writes without tears

> Matthew Wilcox noted that NVMe is specified to have 16KB tear boundaries; he wondered if the SCSI vendors could be convinced into doing something similar

I don't think NVMe in general guarantees anything up to that size, I suspect there might have been some miscommunication somewhere.

See 2.1.4.1 - 2.1.4.2.1 in
https://nvmexpress.org/wp-content/uploads/NVM-Express-NVM...

It imo is pretty clear that a 512 block formatted device may just guarantee that 512 bytes are written in a tear free manner. To guarantee more, awupf would need to be >= 1, which it very commonly isn't.

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Atomic writes without tears

Posted Jun 3, 2024 19:23 UTC (Mon) by willy (subscriber, #9762) [Link]

I think Jake has written down exactly what I said, but that ends up being not what I meant without the surrounding context ;-) We were talking about drives which specify an AWU / AWUPF that is 16KiB (whether that's block-size 4KiB and an AWUPF value of 3 or block-size 512 and an AWUPF of 31).

Basically I was asking that since all implementations of this are cloud storage rather than drive firmware, whether we couldn't just have the cloud storage implement NVMe semantics even with the SCSI command set. Martin doesn't see the need, and since I haven't worked on NVMe in about 12 years, I'm deferring to his expertise.