Slow VM Migration After Upgrade to Version 9

[alistairm]

I have upgraded one of the nodes in my cluster to version 9, I'm now migrating VMs back onto it so I can upgrade the next node but the transfer speed between the Hypervisors is really slow.

• There is a 1Gb dedicated management link to each node.
• The migration starts out using the full 1Gb speed the drops down to less than 1Mb most of the time, sometimes bursting to about 5Mb for a short period.
• CPU and memory load on the server are minimal.
• Migrations before the upgrade were much faster.

I have noticed that this is now showing

~# zpool status
  pool: rpool
 state: ONLINE
status: Some supported and requested features are not enabled on the pool.
        The pool can still be used, but some features are unavailable.
action: Enable all features using 'zpool upgrade'. Once this is done,
        the pool may no longer be accessible by software that does not support
        the features. See zpool-features(7) for details.
  scan: scrub repaired 0B in 00:00:12 with 0 errors on Sun Sep 14 00:24:13 2025
config:

        NAME                                                     STATE     READ WRITE CKSUM
        rpool                                                    ONLINE       0     0     0
          mirror-0                                               ONLINE       0     0     0
            ata-SAMSUNG_MZ7L3480HCHQ-00A07_S664NE0RC34870-part3  ONLINE       0     0     0
            ata-SAMSUNG_MZ7L3480HCHQ-00A07_S664NE0RC34866-part3  ONLINE       0     0     0

errors: No known data errors

  pool: vm-data-0
 state: ONLINE
status: Some supported and requested features are not enabled on the pool.
        The pool can still be used, but some features are unavailable.
action: Enable all features using 'zpool upgrade'. Once this is done,
        the pool may no longer be accessible by software that does not support
        the features. See zpool-features(7) for details.
  scan: scrub repaired 0B in 00:06:49 with 0 errors on Sun Sep 14 00:30:50 2025
config:

        NAME                                               STATE     READ WRITE CKSUM
        vm-data-0                                          ONLINE       0     0     0
          raidz3-0                                         ONLINE       0     0     0
            ata-SAMSUNG_MZ7L3960HCJR-00A07_S662NE0T315726  ONLINE       0     0     0
            ata-SAMSUNG_MZ7L3960HCJR-00A07_S662NE0T315737  ONLINE       0     0     0
            ata-SAMSUNG_MZ7L3960HCJR-00A07_S662NE0T315745  ONLINE       0     0     0
            ata-SAMSUNG_MZ7L3960HCJR-00A07_S662NE0T315742  ONLINE       0     0     0
            ata-SAMSUNG_MZ7L3960HCJR-00A07_S662NE0T315739  ONLINE       0     0     0
            ata-SAMSUNG_MZ7L3960HCJR-00A07_S662NE0T315738  ONLINE       0     0     0
            ata-SAMSUNG_MZ7L3960HCJR-00A07_S662NE0T315733  ONLINE       0     0     0
            ata-SAMSUNG_MZ7L3960HCJR-00A07_S662NE0T315725  ONLINE       0     0     0

errors: No known data errors

Any help would be hugely appreciated.