measuring swap partition speed

Hello list, I have on a rpi4 a usb3-connected disk partitioned like this:

# gpart show

=>        40  1953525088  da0  GPT  (932G)
           40      532480    1  efi  (260M)
       532520        2008       - free -  (1.0M)
       534528     4194304    2  freebsd-swap  (2.0G)
      4728832     4194304    4  freebsd-swap  (2.0G)
      8923136     4194304    5  freebsd-swap  (2.0G)
     13117440     4194304    6  freebsd-swap  (2.0G)
     17311744     4194304    7  freebsd-swap  (2.0G)
     21506048     4194304    8  freebsd-swap  (2.0G)
     25700352  1927823360    3  freebsd-zfs  (920G)
   1953523712        1416       - free -  (708K)

If processes swap out, it runs like a slug [1]. I'd like to test if it's
the disk on its way out. How would I test swap partitions? [2]

[1] it didn't always run like a slug.
[2] would nfs-mounted swap be faster? (1G network)
[3] swap is not encrypted
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