Provided by: nbdkit_1.16.2-1ubuntu3_amd64
nbdkit-fua-filter - nbdkit FUA filter
nbdkit --filter=fua plugin [fuamode=MODE] [plugin-args...]
"nbdkit-fua-filter" is a filter that intentionally modifies handling of the 'Forced Unit Access' (FUA) flag across the NBD protocol. It is mainly useful for testing client or server fallbacks, and for evaluating timing differences between proper use of FUA compared to a full flush.
fuamode=none fuamode=emulate fuamode=native fuamode=force Optional, controls which mode the filter will use. Mode none (default) means that FUA support is not advertised to the client. Mode emulate causes the filter to emulate FUA support using the plugin's "flush" callback, regardless of whether the plugin itself supports more efficient FUA (or refuses to load if the plugin's "can_flush" callback returns false). Mode native causes the filter to advertise native FUA support to earlier filters, useful for comparing optimizations of FUA handling when splitting large requests into sub-requests (or refuses to load if the plugin's "can_fua" callback returns "NBDKIT_FUA_NONE"). Mode force causes the filter to request FUA on all write transactions, even when the client did not request it, and in turn treats client flush requests as a no-op (or refuses to load if the plugin's "can_fua" callback returns "NBDKIT_FUA_NONE").
Serve the file disk.img, but force the client to submit explicit flush requests instead of using "NBD_CMD_FLAG_FUA": nbdkit --filter=fua file disk.img Observe that the blocksize filter optimizes its handling of the FUA flag based on whether it knows nbdkit will be emulating FUA with a flush, by comparing the log filter output on top of different fua filter modes: nbdkit --filter=blocksize --filter=log --filter=fua file disk.img \ maxlen=4k logfile=fua_emulated fuamode=emulate nbdkit --filter=blocksize --filter=log --filter=fua file disk.img \ maxlen=4k logfile=fua_native fuamode=native Serve the file disk.img in write-through mode, where all writes from the client are immediately flushed to disk as if the client had always requested FUA: nbdkit --filter=fua file fuamode=force disk.img
$filterdir/nbdkit-fua-filter.so The filter. Use "nbdkit --dump-config" to find the location of $filterdir.
"nbdkit-fua-filter" first appeared in nbdkit 1.2.
nbdkit(1), nbdkit-file-plugin(1), nbdkit-filter(3), nbdkit-blocksize-filter(1), nbdkit-log-filter(1), nbdkit-nocache-filter(1), nbdkit-noextents-filter(1), nbdkit-noparallel-filter(1), nbdkit-nozero-filter(1).
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