Add `zstream redup` command to convert deduplicated send streams
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
2020-04-10 17:39:55 +00:00
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include $(top_srcdir)/config/Rules.am
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sbin_PROGRAMS = zstream
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zstream_SOURCES = \
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zstream.c \
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zstream.h \
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zstream_dump.c \
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zstream_redup.c
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zstream_LDADD = \
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$(top_builddir)/lib/libnvpair/libnvpair.la \
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2020-05-09 17:17:08 +00:00
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$(top_builddir)/lib/libzfs_core/libzfs_core.la \
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Add `zstream redup` command to convert deduplicated send streams
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
2020-04-10 17:39:55 +00:00
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$(top_builddir)/lib/libzfs/libzfs.la
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