>>>>> "Ted" == Theodore Ts'o <tytso@xxxxxxx> writes: Ted> Ultimately the storage device (or host OS) can always decide to Ted> deprovision the space if it is given a write of all zeroes; there's Ted> nothing in the specs that say anything at all about performance Ted> considerations, or what the back-end storage decides to do in order Ted> to handle a particular write command, so long as a subsequent read Ted> returns the correct data. Well, that has changed a bit with the logical block provisioning bits in SCSI. That's why I brought up the allocation/deallocation assumptions in the existing two blkdev_issue_foo() calls. Ted> Does that make sense? Yeah. So deprovision with guaranteed zero on read is what you're after. I'll chew on that a bit tomorrow. Ted> What does "anchored" mean? Does is it the equivalent of using Ted> fallocate() to allocate the block, but it's marked uninitialized so Ted> any attempt to read it returns zeroes? It means that any allocations internal to the storage device which are required to subsequently perform a write to that block have been made. So it's a way to reserve space without actually writing the blocks. Whether reading an anchored block returns zeroes or something else depends on the usual twisted maze of conflicting and confusing flags. -- Martin K. Petersen Oracle Linux Engineering -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
