Am 28.09.2015 um 05:29 hat Jeff Cody geschrieben: > During mirror, if the target device does not have support zero > initialization, a mirror may result in a corrupt image. > > For instance, on mirror to a host device with format = raw, whatever > random data is on the target device will still be there for unallocated > sectors. > > This is because during the mirror, we set the dirty bitmap to copy only > sectors allocated above 'base'. In the case of target devices where we > cannot assume unallocated sectors will be read as zeroes, we need to > explicitely zero out this data. > > In order to avoid zeroing out all sectors of the target device prior to > mirroring, we do zeroing as part of the block job. A second dirty > bitmap cache is created, to track sectors that are unallocated above > 'base'. These sectors are then checked for status of BDRV_BLOCK_ZERO > on the target - if they are not, then zeroes are explicitly written. > > This only occurs under two conditions: > > 1. 'mode' != "existing" > 2. bdrv_has_zero_init(target) == NULL > > We perform the mirroring through mirror_iteration() as before, except > in two passes. If the above two conditions are met, the first pass > is using the bitmap tracking unallocated sectors, to write the needed > zeroes. Then, the second pass is performed, to mirror the actual data > as before. > > If the above two conditions are not met, then the first pass is skipped, > and only the second pass (the one with the actual data) is performed. > > Signed-off-by: Jeff Cody <jc...@redhat.com>
Also, this makes qemu-iotests 097 fail for me. Kevin
