3 nbdkit-readahead-filter - prefetch data when reading sequentially
7 nbdkit --filter=readahead plugin
11 C<nbdkit-readahead-filter> is a filter that prefetches data when the
12 client is reading sequentially.
14 A common use for this filter is to accelerate sequential copy
15 operations (like S<C<qemu-img convert>>) when plugin requests have a
16 high overhead (like L<nbdkit-curl-plugin(1)>). For example:
18 nbdkit -U - --filter=readahead curl https://example.com/disk.img \
19 --run 'qemu-img convert $nbd disk.img'
21 The filter uses a simple adaptive algorithm which accelerates
22 sequential reads, but has a small penalty if the client does random
23 reads. If the client mixes reads with writes or write-like operations
24 (trimming, zeroing) then it will work but there can be a large
29 There are no parameters specific to nbdkit-readahead-filter. Any
30 parameters are passed through to and processed by the underlying
31 plugin in the normal way.
37 =item F<$filterdir/nbdkit-readahead-filter.so>
41 Use C<nbdkit --dump-config> to find the location of C<$filterdir>.
47 C<nbdkit-readahead-filter> first appeared in nbdkit 1.12.
52 L<nbdkit-cache-filter(1)>,
53 L<nbdkit-curl-plugin(1)>,
54 L<nbdkit-retry-filter(1)>,
55 L<nbdkit-ssh-plugin(1)>,
56 L<nbdkit-vddk-plugin(1)>,
66 Copyright (C) 2019 Red Hat Inc.