On 24.09.2016 19:44, Vladimir Sementsov-Ogievskiy wrote: > On 24.09.2016 19:35, Alex Bligh wrote: >>> On 24 Sep 2016, at 17:20, Vladimir Sementsov-Ogievskiy >>> <[email protected]> wrote: >>> >>> Also, accordingly to documentation, NBD_CMD_TRIM is not appropriate >>> for disk clearing: >>> >>> * `NBD_CMD_TRIM` (4) >>> >>> A hint to the server that the data defined by len and offset >>> is no >>> longer needed. A server MAY discard len bytes starting at >>> offset, but >>> is not required to. >>> >>> After issuing this command, a client MUST NOT make any >>> assumptions >>> about the contents of the export affected by this command, until >>> overwriting it again with `NBD_CMD_WRITE`. >>> >>> - it may do nothing.. So, what to do with this? add flag FORCE_TRIM >>> for this command? Or add FORCE_HOLES flag to WRITE_ZEROES? >> You cannot force a hole, because NBD the is not guaranteed to support >> holes. >> >> Use NBD_CMD_WRITE_ZEROES without NBD_CMD_FLAG_NO_HOLE and you can >> pretty much assume that a server that supports holes will write >> holes. A server that does not support holes will write zeroes. If you >> don't care whether the resultant data is zero, just use NBD_CMD_TRIM. >> But as you do care (see above) you must be prepared for a 'thick' >> write of zeroes on servers that don't support it. >> > > No, holes are critical. Concreate case: incremental backup to delta > file. If we write zeroes instead of holes, we will lose underlying > data (from previous incremental). > hmm, no, sorry, that is not needed.
-- Best regards, Vladimir ------------------------------------------------------------------------------ _______________________________________________ Nbd-general mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/nbd-general
