On 23.10.2019 14:08, Gionatan Danti wrote: > > For example, consider a completely filled 64k chunk thin volume (with > thinpool having ample free space). Snapshotting it and writing a 4k > block on origin will obviously cause a read of the original 64k chunk, > an in-memory change of the 4k block and a write of the entire modified > 64k block to a new location. But writing, say, a 1 MB block should *not* > cause the same read on source: after all, the read data will be > immediately discarded, overwritten by the changed 1 MB block. > > However, my testing shows that source chunks are always read, even when > completely overwritten. Not only read but sometimes write. I watched it without snapshot. Only zeroing was enabled. Before wrote new chunks "dd bs=1048576 ..." chunks were zeroed. But for security it's good. IMHO: In this case good choice firstly write chunks to the disk and then give this chunks to the volume. > > Am I missing something? >
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