On Feb 12 00:37, Keith Busch wrote: > On Thu, Feb 11, 2021 at 09:43:05AM +0100, Klaus Jensen wrote: > > On Feb 11 12:37, Keith Busch wrote: > > > > > Is there a use case with a real qemu guest wanting this? > > > > Like for the extended metadata case (which also does not have a lot of > > "public" exposure, but definitely have enterprise use), our main > > motivation here was to ease testing for compliance suites and frameworks > > like SPDK. > > I'm okay with the metadata patches. > > > I'm honestly have no clue what so ever what a real world use > > of Write Uncorrectable would be. It's been in the spec since 1.0, so > > there must have been some reason, Is it just to align with SCSI WRITE > > LONG? I'm not SCSI expert at all, but from what I can read it looks like > > that was also intended as a feature for testing read error conditions. > > I don't think it's for testing purposes. > > If you need to send a burst of non-atomic writes (ex: writing a RAID > stripe), a power failure can result in an inconsistent state where you > don't know at a block level which ones have old data or new data. If you > Write Uncorrectable first, you can never read old data, and thus have no > "write hole". > > Journalling solves this better, and I'm not aware of any real > implementation relying on uncorrectable.
Right, thanks! I'm aware of the RAID write hole issue, but I did not consider Write Uncorrectable as a possible means to solve it.
signature.asc
Description: PGP signature
