Re: [RFC 0/3] Btrfs checksum offload

[Kanchan Joshi <joshi.k@samsung.com>]

On 1/31/2025 1:51 AM, Martin K. Petersen wrote:
>> There is value in avoiding Copy-on-write (COW) checksum tree on a
>> device that can anyway store checksums inline (as part of PI). This
>> would eliminate extra checksum writes/reads, making I/O more
>> CPU-efficient. Additionally, usable space would increase, and write
>> amplification, both in Btrfs and eventually at the device level, would
>> be reduced [*].
> I have a couple of observations.
> 
> First of all, there is no inherent benefit to PI if it is generated at
> the same time as the ECC. The ECC is usually far superior when it comes
> to protecting data at rest. And you'll still get an error if uncorrected
> corruption is detected. So BLK_INTEGRITY_OFFLOAD_NO_BUF does not offer
> any benefits in my book.

I fully agree, there is no benefit if we see it from E2E use case.
But for a different use case (i.e., checksum offload), 
BLK_INTEGRITY_OFFLOAD_NO_BUF is as good as it gets.

[Application -> FS -> Block-layer -> Device]

I understand that E2E gets stronger when integrity/checksum is placed at 
the origin of data (application), and then each component collaborates 
in checking it.

But I am not doing E2E here. Call it abuse or creative, but I am using 
the same E2E capable device to do checksum-offload. If the device had 
exposed checksum-offload in a different way, I would have taken that 
route rather than E2E one.