Comment 0 for bug 1890979

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haixin (haixin77) wrote : Optimize volume copy logic

when we migration, retype or backup an volume, it need to call _transfer_data function in, especially in the RBD volume that we use a lot.

   if the volume is thin volume, an the file in the volume is sparse file, this means it may not the end of file when we read b'',if we break here will lead to Incomplete file,This is a serious situation for mirror image。
   so we should not break, we should continue and seek the offset of dest. in order to get the full data of src volume.