It does not need configuring and speeds up the process of requesting extents if the client asks for them one by one (like qemu-img). Signed-off-by: Martin Kletzander <mkletzan(a)redhat.com&gt; --- Essentially a v2 of the following patch since now there is a probing function: https://www.redhat.com/archives/libguestfs/2019-September/msg00249.html v2v/nbdkit.ml | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/v2v/nbdkit.ml b/v2v/nbdkit.ml index 89fca337cbaa..77d2a506dc41 100644 --- a/v2v/nbdkit.ml +++ b/v2v/nbdkit.ml @@ -169,6 +169,13 @@ let common_create ?bandwidth plugin_name plugin_args plugin_env = ) else [] in + (* Caching extents speeds up qemu-img, especially its consecutive + block_status requests with req_one=1. + *) + if probe_filter "cacheextents" then ( + add_arg "--filter"; add_arg "cacheextents" + ); + (* Retry filter (if it exists) can be used to get around brief * interruptions in service. It must be closest to the plugin. *)