[Libguestfs] [PATCH libnbd 3/3] copy: Update nbdcopy(1) about multiple connections
Using multiple connections does not depend now on NBD multi-conn flag.
Add a note about using --shared=4 in qemu-nbd to allow multiple
connections.
Signed-off-by: Nir Soffer <nsoffer(a)redhat.com>
---
copy/nbdcopy.pod | 25 +++++++------------------
1 file changed, 7 insertions(+), 18 deletions(-)
diff --git a/copy/nbdcopy.pod b/copy/nbdcopy.pod
index f710093..781bb10 100644
--- a/copy/nbdcopy.pod
+++ b/copy/nbdcopy.pod
@@ -103,10 +103,9 @@ output on the destination.
=item B<--connections=>N
-Set the maximum number of NBD connections ("multi-conn"). By default
-nbdcopy will try to use multi-conn with up to 4 connections if the NBD
-server supports it. If copying between NBD servers then nbdcopy
-cannot use multi-conn if either of the servers does not support it.
+Set the maximum number of NBD connections. By default nbdcopy will try
+to use multiple connections with up to 4 connections. Some servers
+like L<qemu-nbd(8)> support only one connection by default.
=item B<--destination-is-zero>
@@ -216,23 +215,13 @@ pipe, or a socket, or if you use the I<--synchronous> option,
then
nbdcopy works in synchronous mode with no parallelism, and nothing
else in this section applies.
-The I<--connections=N> option controls NBD multi-conn (see
-L<libnbd(3)/Multi-conn>), opening up to N connections to the NBD
+The I<--connections=N> option open up to N connections to the NBD
server (or to both NBD servers if copying between NBD servers). This
-defaults to 4. The NBD servers must support and advertise multi-conn.
-For L<nbdkit(1)> availability of multi-conn can depend on the plugin.
-You can use L<nbdinfo(1)> to find out if a particular NBD server is
-advertising multi-conn. If the NBD server doesn’t advertise
-multi-conn then only one connection will be opened regardless of the
-I<--connections> flag.
-
-When copying between two NBD servers, the number of connections is
-limited to the minimum multi-conn supported on both sides. For the
-purposes of this calculation, you can consider local files and block
-devices as supporting infinite multi-conn.
+defaults to 4. When using L<qemu-nbd(8)> you need to enable multiple
+conections using the I<--shared=4> command line option.
When you run an NBD server as a subprocess (using the S<C<[ ... ]>>
-syntax) multi-conn cannot be used.
+syntax) multiple connections cannot be used.
The I<--threads=N> option allows nbdcopy to start up to N threads
(defaulting to the number of cores). However nbdcopy cannot use more
--
2.26.3