Hello! Last time when I going to removing and creating lun on CTLD, I have this problem on some concrete targets:

ctladm: LUN removal error: LUN 41 is not managed by the block backend
ctladm: LUN creation error: ctl_add_lun() returned error 28, see dmesg for details
LUN 91 removed successfully
LUN created successfully
backend:       block
device type:   0
LUN size:      966367641600 bytes
blocksize      512 bytes
LUN ID:        91
Serial Number: SER91
Device ID:     DEV91
LUN 141 removed successfully
LUN created successfully
backend:       block
device type:   0
LUN size:      966367641600 bytes
blocksize      512 bytes
LUN ID:        141
Serial Number: SER141
Device ID:     DEV141

This code remove and create LUNs: 

ctladm remove -b block -l $name
zfs destroy -R ssd/orig/original$c@win$name
zfs snap ssd/orig/original$c@win$name
zfs clone ssd/orig/original$c@win$name ssd/snap/win$name
ctladm create -b block -l $name -o file=/dev/zvol/ssd/snap/win$name -o uuid=1d48547e-0d9d-492f-8878-9054d1be7$a -S SER$name -d DEV$name -o vendor=MICRON

ctladm remove -b block -l $a
zfs destroy -R online/orig/online@win$name
zfs snap online/orig/online@win$name
zfs clone online/orig/online@win$name online/snap/win$name
ctladm create -b block -l $a -o file=/dev/zvol/online/snap/win$name -o uuid=2d48547e-0d9d-492f-8878-9054d1be7$a -S SER$a -d DEV$a -o vendor=SAMSUNG

ctladm remove -b block -l $b 
zfs destroy -R hdd/orig/games@win$name
zfs snap hdd/orig/games@win$name
zfs clone hdd/orig/games@win$name hdd/snap/win$name
ctladm create -b block -l $b -o file=/dev/zvol/hdd/snap/win$name -o uuid=3d48547e-0d9d-492f-8878-9054d1be7$b -S SER$b -d DEV$b -o vendor=HYNIX

It's ctl.conf:

target iqn.pc1 { 
auth-group no-authentication 
portal-group xxx 
lun 0 { 
path /dev/zvol/ssd/snap/win1 
ctl-lun 1}
lun 1 { 
path /dev/zvol/online/snap/win1 
ctl-lun 51}
lun 2 { 
path /dev/zvol/hdd/snap/win1 
ctl-lun 101}}
target iqn.pc2 { 
auth-group no-authentication 
portal-group xxx 
lun 0 { 
path /dev/zvol/ssd/snap/win2 
ctl-lun 2}
lun 1 { 
path /dev/zvol/online/snap/win2 
ctl-lun 52}
lun 2 { 
path /dev/zvol/hdd/snap/win2 
ctl-lun 102}}

config ZFS:
dedup=off
compress=lz4
atime=off
sync=disabled
secondarycache=none
primarycache=all

Server hardware:
xeon E5-2670
128Gb DDR3 ECC REG
10Gb NIC
SSD for system
2 nvme SSDs for zpools

Maybe you have some answers for my questions, thanks!