Hi Chuck! > The purpose of WRITE_SAME is to demark the database blocks with > sentinels on each end of the database block containing a time > stamp or hash. SCSI WRITE SAME writes a contiguous range of logical blocks. Each block will be filled with the contents of the single logical block data buffer provided as payload. So with SCSI WRITE SAME it's not possible to write a 512-byte sentinel, followed by 15KB of zeroes, followed by a 512-byte sentinel in a single operation. You'd have to do a 16KB WRITE SAME with a zeroed payload followed by a two individual WRITEs for the sentinels. Or fill the entire 16KB application block with the same repeating 512-byte pattern. I'm not familiar with NFS v4.2 WRITE SAME. But it sounds like it allows the application to define a block larger than the logical block size of the underlying storage. Is that correct? If so, there would not be a direct mapping between NFS WRITE SAME and SCSI ditto. As Christoph pointed out, NVMe doesn't have WRITE SAME. And we removed support in the block layer a while back. That doesn't prevent implementing WRITE SAME capability in NFS, of course. It just sounds like the NFS semantics are different enough that aligning to SCSI is not applicable. -- Martin K. Petersen Oracle Linux Engineering
