On Thu, Mar 03, 2016 at 01:01:11PM -0500, Martin K. Petersen wrote: > That's not entirely true. Writing the blocks may cause them to be > allocated on the storage device (depending on which flags we feed it in > WRITE SAME). > > The filesystems people were wanted the following semantics: > > - deallocate, don't care about contents for future reads (discard) > - deallocate, guarantee zeroes on future reads (zeroout) > - (re)allocate, guarantee zeroes on future reads (zeroout) > > Maybe we just need a better naming scheme...
In filesystem terms we have two and three: - FALLOC_FL_PUNCH_HOLE assures zeroes are returned, but space is deallocated as much as possible - FALLOC_FL_ZERO_RANGE assures zeroes are returned, AND blocks are actually allocated Returning stale blocks in a file system is a nasty security risk, so we don't do that, and so shouldn't storage that offers any kind of multi tenancy, and if it's just VMs using multiple partitions on it.
