why the children dataset consume so much data, how could I delete that?
Dataset Name
Used / Available
Encryption
Roles
NAS
969.07 GiB / 1023.9 MiB
Unencrypted
ix-applications
4.26 GiB / 2.57 TiB
Unencrypted
NAS
865.62 GiB / 2.57 TiB
Unencrypted
Sigh. 
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You might be want to post screenshots or photos of the GUI window. If you are running CLI or command line interface commands, you can post it back using preformatted text (</> or Ctrl+e) on the reply box or text window.
What applications do you have and where are you storing their data? You need to give us as much info as possilble. We can only go off what is provided and canāt see what you see on the system.
i cannot import the media
ix-applications for tailscale and immich
my smb share used to be 3.5tb but now is 2.5
Immich is probably storing itās data in ix-applications and not in an outside dataset. Check your Immich configuration.
You will have to use the command line (CLI) to look through those folders and see what is taking up disk space. You might have some luck browsing the forums for āImmichā and any disk space related posts.
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I think we can all appreciate that English is probably not your main language, but you are really not giving us the information we need to help you. Can you please open a command shell and run the following commands, and then copy and paste the responses from each command into its own </> box here:
lsblk -bo NAME,LABEL,MAJ:MIN,TRAN,ROTA,ZONED,VENDOR,MODEL,SERIAL,PARTUUID,START,SIZE,PARTTYPENAME/sbin/zpool status -vLtsc lsblk,serial,smartx,smartsudo zpool import/sbin/zpool list -v/sbin/zfs list
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where is the shell in immich or just click the shell in menu of truenas?
TrueNAS shell.
truenas_admin@truenas[~]$ lsblk -bo NAME,LABEL,MAJ:MIN,TRAN,ROTA,ZONED,VENDOR,MODEL,SERIAL,PARTUUID,START,SIZE,PARTTYPENAME
NAME LABEL MAJ:MIN TRAN ROTA ZONED VENDOR MODEL SERIAL PARTUUID START SIZE PARTTYPENAME
sda 8:0 sata 1 none ATA ST4000VN008-2DR166 Z9LNNEXE 4000787030016
āāsda1 NAS 8:1 1 none 99ad68ee-5241-4152-aceb-eadcfbc4bd23 4096 4000784056832 Solaris /usr & Apple ZFS
sdb 8:16 sata 1 none ATA ST4000VN008-2DR166 Z9LNNFVO 4000787030016
āāsdb1 NAS 8:17 1 none ba0e22b7-62a3-4cca-945b-ad6855684409 4096 4000784056832 Solaris /usr & Apple ZFS
nvme0n1 259:0 nvme 0 none KINGBANK KP230 LJ6232R012265 120034123776
āānvme0n1p1 259:1 nvme 0 none 55c33583-f4db-11ee-8b26-00e269671c74 40 272629760 EFI System
āānvme0n1p2 boot-pool 259:2 nvme 0 none 55c6d2b7-f4db-11ee-8b26-00e269671c74 34086952 102575898624 FreeBSD ZFS
āānvme0n1p3 259:3 nvme 0 none 55c55efe-f4db-11ee-8b26-00e269671c74 532520 17179869184 FreeBSD swap
truenas_admin@truenas[~]$ sudo zpool import
[sudo] password for truenas_admin:
no pools available to import
truenas_admin@truenas[~]$ /sbin/zpool list -v
NAME SIZE ALLOC FREE CKPOINT EXPANDSZ FRAG CAP DEDUP HEALTH ALTROOT
NAS 3.62T 822G 2.82T - - 8% 22% 1.00x ONLINE /mnt
mirror-0 3.62T 822G 2.82T - - 8% 22.1% - ONLINE
99ad68ee-5241-4152-aceb-eadcfbc4bd23 3.64T - - - - - - - ONLINE
ba0e22b7-62a3-4cca-945b-ad6855684409 3.64T - - - - - - - ONLINE
boot-pool 95.5G 6.51G 89.0G - 16G 29% 6% 1.00x ONLINE -
nvme0n1p2 95.5G 6.51G 89.0G - 16G 29% 6.81% - ONLINE
truenas_admin@truenas[~]$ /sbin/zfs list
NAME USED AVAIL REFER MOUNTPOINT
NAS 822G 2.71T 104K /mnt/NAS
NAS/NAS 782G 2.71T 782G /mnt/NAS/NAS
NAS/ix-apps 40.3G 2.71T 112K /mnt/.ix-apps
NAS/ix-apps/app_configs 7.95M 2.71T 7.95M /mnt/.ix-apps/app_configs
NAS/ix-apps/app_mounts 149M 2.71T 96K /mnt/.ix-apps/app_mounts
NAS/ix-apps/app_mounts/immich 149M 2.71T 96K /mnt/.ix-apps/app_mounts/immich
NAS/ix-apps/app_mounts/immich/data 14.8M 2.71T 14.8M /mnt/.ix-apps/app_mounts/immich/data
NAS/ix-apps/app_mounts/immich/postgres_data 134M 2.71T 134M /mnt/.ix-apps/app_mounts/immich/postgres_data
NAS/ix-apps/app_mounts/tailscale 300K 2.71T 96K /mnt/.ix-apps/app_mounts/tailscale
NAS/ix-apps/app_mounts/tailscale/state 204K 2.71T 136K /mnt/.ix-apps/app_mounts/tailscale/state
NAS/ix-apps/docker 40.0G 2.71T 40.0G /mnt/.ix-apps/docker
NAS/ix-apps/truenas_catalog 190M 2.71T 190M /mnt/.ix-apps/truenas_catalog
boot-pool 6.51G 86.0G 24K none
boot-pool/.system 1.56G 86.0G 1.55G legacy
boot-pool/.system/configs-ae32c386e13840b2bf9c0083275e7941 24K 86.0G 24K legacy
boot-pool/.system/cores 24K 1024M 24K legacy
boot-pool/.system/netdata-ae32c386e13840b2bf9c0083275e7941 11.5M 86.0G 11.5M legacy
boot-pool/.system/nfs 28K 86.0G 28K legacy
boot-pool/.system/samba4 78K 86.0G 78K legacy
boot-pool/ROOT 4.85G 86.0G 24K none
boot-pool/ROOT/24.10.0 2.37G 86.0G 165M legacy
boot-pool/ROOT/24.10.0/conf 6.50M 86.0G 6.50M /conf
boot-pool/ROOT/24.10.0/data 7.50M 86.0G 7.50M /data
boot-pool/ROOT/24.10.0/etc 3.60M 86.0G 3.20M /etc
boot-pool/ROOT/24.10.0/home 31K 86.0G 31K /home
boot-pool/ROOT/24.10.0/usr 1.80G 86.0G 1.80G /usr
boot-pool/ROOT/24.10.0/var 393M 86.0G 18.5M /var
boot-pool/ROOT/24.10.0/var/ca-certificates 24K 86.0G 24K /var/local/ca-certificates
boot-pool/ROOT/24.10.0/var/log 374M 86.0G 371M /var/log
boot-pool/ROOT/24.10.0/var/log/journal 3.75M 86.0G 3.75M /var/log/journal
boot-pool/ROOT/25.04.1-2 2.48G 86.0G 173M legacy
boot-pool/ROOT/25.04.1-2/audit 1.18M 86.0G 1.18M /audit
boot-pool/ROOT/25.04.1-2/conf 6.70M 86.0G 6.70M /conf
boot-pool/ROOT/25.04.1-2/data 7.49M 86.0G 7.49M /data
boot-pool/ROOT/25.04.1-2/etc 3.47M 86.0G 3.06M /etc
boot-pool/ROOT/25.04.1-2/home 31.5K 86.0G 31.5K /home
boot-pool/ROOT/25.04.1-2/mnt 25K 86.0G 25K /mnt
boot-pool/ROOT/25.04.1-2/opt 24K 86.0G 24K /opt
boot-pool/ROOT/25.04.1-2/root 127K 86.0G 127K /root
boot-pool/ROOT/25.04.1-2/usr 2.27G 86.0G 2.27G /usr
boot-pool/ROOT/25.04.1-2/var 28.8M 86.0G 3.91M /var
boot-pool/ROOT/25.04.1-2/var/ca-certificates 24K 86.0G 24K /var/local/ca-certificates
boot-pool/ROOT/25.04.1-2/var/lib 15.3M 86.0G 15.2M /var/lib
boot-pool/ROOT/25.04.1-2/var/lib/incus 24K 86.0G 24K /var/lib/incus
boot-pool/ROOT/25.04.1-2/var/log 9.20M 86.0G 2.91M /var/log
boot-pool/ROOT/25.04.1-2/var/log/journal 6.29M 86.0G 6.29M /var/log/journal
boot-pool/grub 1.91M 86.0G 1.91M legacy
truenas_admin@truenas[~]$ /sbin/zpool status -vLtsc lsblk,serial,smartx,smart
pool: NAS
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 01:29:00 with 0 errors on Sun Jun 15 01:29:02 2025
config:
NAME STATE READ WRITE CKSUM SLOW size vendor model serial hours_on pwr_cyc health realloc rep_ucor cmd_to temp pend_sec off_ucor ata_err nvme_err
NAS ONLINE 0 0 0 -
mirror-0 ONLINE 0 0 0 -
sda1 ONLINE 0 0 0 0 3.6T ATA ST4000VN008-2DR166 Z9LNNEXE 10105 18 PASSED 0 0 0 36 0 0 - - (trim unsupported)
sdb1 ONLINE 0 0 0 0 3.6T ATA ST4000VN008-2DR166 Z9LNNFVO 10105 17 PASSED 0 0 0 36 0 0 - - (trim unsupported)
errors: No known data errors
pool: boot-pool
state: ONLINE
status: One or more features are enabled on the pool despite not being
requested by the 'compatibility' property.
action: Consider setting 'compatibility' to an appropriate value, or
adding needed features to the relevant file in
/etc/zfs/compatibility.d or /usr/share/zfs/compatibility.d.
scan: scrub repaired 0B in 00:00:57 with 0 errors on Tue Jun 24 03:45:59 2025
config:
NAME STATE READ WRITE CKSUM SLOW size vendor model serial hours_on pwr_cyc health realloc rep_ucor cmd_to temp pend_sec off_ucor ata_err nvme_err
boot-pool ONLINE 0 0 0 -
nvme0n1p2 ONLINE 0 0 0 0 111.8G - KINGBANK KP230 LJ6232R012265 17622 268 PASSED - - - 42 - - - 0 (untrimmed)
errors: No known data errors
Can you do a screenshot of the GUI where you think there is a problem with āChildrenā? Try to do almost the entire TrueNAS GUI so we can see what sections, windows and data you are looking at.
I am guessing your root pool is called NAS and you have a child dataset named NAS and that is what you think is the problem?
so i solve the problem by deled dataset and make a new one I have backuped the data thank you for solving my truenas problem
Anytime. It was a pleasure.
TL;DR summary
I think that this is simply a misunderstanding of what āavailable spaceā means - it means free space available for more data and NOT total space, so I donāt think that there is any technical problem, and so backing everything up and destroying / recreating the pool will not do anything.
Analysis
The pool consists of a mirror of 2x 4TB Ironwolf HDDs - converting this to TiB by deducting 9% means there will be c. 3.64TiB of useable space in the pool - thatās the total space in the pool - and this is what the zpool list shows.
The NAS/NAS dataset has 732GiB of data in it - but you also need to add to this the space used by the hidden TrueNAS ix-apps dataset (as shown by the zfs list command) which is using 40.3GiB. Total used is thus 822GiB or 0.822TiB and deducting this from 3.64TiB leaves you c. 2.82TiB and this is exactly what is shown in the zpool list. Yes - this is different from the 2.71TiB shown as being free in the zfs list and UI, however that can be accounted for by e.g. zfs list only estimating the amount of data that can be stored (whereas zpool list shows the accurate count of blocks that are free) and I am guessing that it is estimating e.g. metadata overheads.
So, I donāt think that there is any technical problem to be resolved.
P.S.
Lol. Literally all you did was sigh at the very beginning of the thread!!! 
See here.
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