On Wed, 05/06 10:59, Paolo Bonzini wrote: > > > On 06/05/2015 03:45, Fam Zheng wrote: > >> > This is not enough, you also have to do the discard in block/mirror.c, > >> > otherwise the destination image could even become fully provisioned! > > I wasn't sure what if src and dest have different > > can_write_zeroes_with_unmap > > value, but your argument is stronger. > > > > I will add discard in mirror. Besides that, do we need to compare the > > can_write_zeroes_with_unmap? > > Hmm, if can_write_zeroes_with_unmap is set, it's probably better to > write zeroes instead of discarding, in case the guest is relying on it. >
I think there are four cases: # src can_write_zeroes_with_unmap target can_write_zeroes_with_unmap -------------------------------------------------------------------------------- 1 true true 2 true false 3 false true 4 false false I think replicating discard only works for 1, because both side would then read 0. For case 2 & 3 it's probably better to mirror the actual reading of source. I'm not sure about 4. What do you think? Fam
