can I reduce the size of a mirror zpool?

Testing with file-based devices

# Will this work with disk-based devices which use partitions?
# Instead of /tmp/0.raw, using /dev/adap3?

# create some 500M devices:

root@r730-04:/tmp # for i in $(seq 10 13) ; do truncate -s 500M $i.raw ; done

# and some 1G devices:

root@r730-04:/tmp # for i in $(seq 0 3) ; do truncate -s 1G $i.raw ; done


# the devices:

root@r730-04:/tmp # ls -lh /tmp/*.raw
-rw-r--r--  1 root wheel  1.0G Nov 19 18:18 /tmp/0.raw
-rw-r--r--  1 root wheel  1.0G Nov 19 18:18 /tmp/1.raw
-rw-r--r--  1 root wheel  500M Nov 19 18:11 /tmp/10.raw
-rw-r--r--  1 root wheel  500M Nov 19 18:11 /tmp/11.raw
-rw-r--r--  1 root wheel  500M Nov 19 18:18 /tmp/12.raw
-rw-r--r--  1 root wheel  500M Nov 19 18:18 /tmp/13.raw
-rw-r--r--  1 root wheel  1.0G Nov 19 18:14 /tmp/2.raw
-rw-r--r--  1 root wheel  1.0G Nov 19 18:14 /tmp/3.raw



# create a 1GB zpool

root@r730-04:/tmp # zpool destroy test-pool
root@r730-04:/tmp # zpool create test-pool mirror /tmp/0.raw /tmp/1.raw

root@r730-04:/tmp # zpool list test-pool
NAME        SIZE  ALLOC   FREE  CKPOINT  EXPANDSZ   FRAG    CAP  DEDUP    HEALTH  ALTROOT
test-pool   960M  10.4M   950M        -         -     0%     1%  1.00x    ONLINE  -

root@r730-04:/tmp # zpool status test-pool
  pool: test-pool
 state: ONLINE
config:

	NAME            STATE     READ WRITE CKSUM
	test-pool       ONLINE       0     0     0
	  mirror-0      ONLINE       0     0     0
	    /tmp/0.raw  ONLINE       0     0     0
	    /tmp/1.raw  ONLINE       0     0     0

errors: No known data errors
root@r730-04:/tmp # ls -l /test-pool/
total 0
root@r730-04:/tmp # dd if=/dev/random of=/test-pool/random1 bs=1m count=10
10+0 records in
10+0 records out
10485760 bytes transferred in 0.028923 secs (362544700 bytes/sec)
root@r730-04:/tmp # ls -l /test-pool/
total 1
-rw-r--r--  1 root wheel 10485760 Nov 19 18:18 random1
root@r730-04:/tmp # 


# add another mirror to the zpool, with 500M devices

root@r730-04:/tmp # zpool add test-pool mirror /tmp/12.raw /tmp/13.raw

root@r730-04:/tmp # zpool status test-pool
  pool: test-pool
 state: ONLINE
config:

	NAME             STATE     READ WRITE CKSUM
	test-pool        ONLINE       0     0     0
	  mirror-0       ONLINE       0     0     0
	    /tmp/0.raw   ONLINE       0     0     0
	    /tmp/1.raw   ONLINE       0     0     0
	  mirror-1       ONLINE       0     0     0
	    /tmp/12.raw  ONLINE       0     0     0
	    /tmp/13.raw  ONLINE       0     0     0

errors: No known data errors
root@r730-04:/tmp # ls -l /test-pool/
total 10249
-rw-r--r--  1 root wheel 10485760 Nov 19 18:18 random1
root@r730-04:/tmp # 


# remove the bigger mirror:

root@r730-04:/tmp # zpool remove test-pool mirror-0

# the zpool is now smaller

root@r730-04:/tmp # zpool list test-pool
NAME        SIZE  ALLOC   FREE  CKPOINT  EXPANDSZ   FRAG    CAP  DEDUP    HEALTH  ALTROOT
test-pool   480M  11.0M   469M        -         -     0%     2%  1.00x    ONLINE  -
root@r730-04:/tmp # ls -l /test-pool/
total 10249
-rw-r--r--  1 root wheel 10485760 Nov 19 18:18 random1
root@r730-04:/tmp # 


dvl@r730-04:~ $ zpool status test-pool
  pool: test-pool
 state: ONLINE
remove: Removal of vdev 0 copied 10.5M in 0h0m, completed on Wed Nov 19 18:21:45 2025
	384 memory used for removed device mappings
config:

	NAME             STATE     READ WRITE CKSUM
	test-pool        ONLINE       0     0     0
	  mirror-1       ONLINE       0     0     0
	    /tmp/12.raw  ONLINE       0     0     0
	    /tmp/13.raw  ONLINE       0     0     0

errors: No known data errors
dvl@r730-04:~ $