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Deduplicated send and receive is deprecated. To ease migration to the new dedup-send-less world, the commit adds a `zstream redup` utility to convert deduplicated send streams to normal streams, so that they can continue to be received indefinitely. The new `zstream` command also replaces the functionality of `zstreamdump`, by way of the `zstream dump` subcommand. The `zstreamdump` command is replaced by a shell script which invokes `zstream dump`. The way that `zstream redup` works under the hood is that as we read the send stream, we build up a hash table which maps from `<GUID, object, offset> -> <file_offset>`. Whenever we see a WRITE record, we add a new entry to the hash table, which indicates where in the stream file to find the WRITE record for this block. (The key is `drr_toguid, drr_object, drr_offset`.) For entries other than WRITE_BYREF, we pass them through unchanged (except for the running checksum, which is recalculated). For WRITE_BYREF records, we change them to WRITE records. We find the referenced WRITE record by looking in the hash table (for the record with key `drr_refguid, drr_refobject, drr_refoffset`), and then reading the record header and payload from the specified offset in the stream file. This is why the stream can not be a pipe. The found WRITE record replaces the WRITE_BYREF record, with its `drr_toguid`, `drr_object`, and `drr_offset` fields changed to be the same as the WRITE_BYREF's (i.e. we are writing the same logical block, but with the data supplied by the previous WRITE record). This algorithm requires memory proportional to the number of WRITE records (same as `zfs send -D`), but the size per WRITE record is relatively low (40 bytes, vs. 72 for `zfs send -D`). A 1TB send stream with 8KB blocks (`recordsize=8k`) would use around 5GB of RAM to "redup". Reviewed-by: Jorgen Lundman <lundman@lundman.net> Reviewed-by: Paul Dagnelie <pcd@delphix.com> Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov> Signed-off-by: Matthew Ahrens <mahrens@delphix.com> Closes #10124 Closes #10156 |
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