Truenas mount /var/db/system on pool

[matt.anti]

Hi everybody,
I would like to ask why truenas mounts the /var/db/system path on the disk pool I created.

I realized it as I tried to simulate the degradation of zraid2 by removing 4 disks, once removed the webui was no longer reachable.

I then logged into the machine via ssh and this is what I found

Code:

root@truenas[~]# df -h
Filesystem                                                               Size    Used   Avail Capacity  Mounted on
boot-pool/ROOT/default                                                   108G    1.2G    106G     1%    /
devfs                                                                    1.0K    1.0K      0B   100%    /dev
tmpfs                                                                     32M     10M     22M    33%    /etc
tmpfs                                                                    4.0M    8.0K    4.0M     0%    /mnt
tmpfs                                                                     43G     25M     43G     0%    /var
fdescfs                                                                  1.0K    1.0K      0B   100%    /dev/fd
storage_nodes_05_d01                                                     4.1T    192K    4.1T     0%    /mnt/storage_nodes_05_d01
storage_nodes_05_d01/.system                                             4.1T    240K    4.1T     0%    /var/db/system
storage_nodes_05_d01/.system/cores                                       1.0G    192K    1.0G     0%    /var/db/system/cores
storage_nodes_05_d01/.system/samba4                                      4.1T    344K    4.1T     0%    /var/db/system/samba4
storage_nodes_05_d01/.system/syslog-481d11dc8be44177a340c08096234a34     4.1T    384K    4.1T     0%    /var/db/system/syslog-481d11dc8be44177a340c08096234a34
storage_nodes_05_d01/.system/rrd-481d11dc8be44177a340c08096234a34        4.1T     23M    4.1T     0%    /var/db/system/rrd-481d11dc8be44177a340c08096234a34
storage_nodes_05_d01/.system/configs-481d11dc8be44177a340c08096234a34    4.1T    192K    4.1T     0%    /var/db/system/configs-481d11dc8be44177a340c08096234a34
storage_nodes_05_d01/.system/webui                                       4.1T    192K    4.1T     0%    /var/db/system/webui
storage_nodes_05_d01/.system/services                                    4.1T    192K    4.1T     0%    /var/db/system/services

can you help me understand why?

Thanks

 

[Samuel Tai]

This is historical. The system dataset is where TrueNAS keeps its logs, GELI keys, and Samba runtime data (for Active Directory). Back when TrueNAS was FreeNAS, and the boot volumes were small USB thumb drives, the system dataset had to be stored in the data pool due to the limited capacity and endurance of thumb drives. As most data pools also have much better redundancy and performance (mirrors or RAIDZx) than a single or a mirrored pair of thumb drives, the system dataset was also safer on the data pool.

 

[sretalla]

It's automatically moved off the boot pool as soon as you have a data pool.

After that, you can opt to move it where it makes sense... for some folks who run boot pools on SSDs, it's often fine to move back to the boot pool. System | System Dataset...

 

[matt.anti]

Thanks all for the reply