Help me understand behaviour of full datasets

[Chuu]

I am experimenting with FreeNAS on a Hyper-V VM with eight 3GB disks in RaidZ3. My pool looks something like this: (ignore the scrub issue -- I intentionally introduced corruption in a previous test)

Code:

root@freenas:/ # zpool status -v
  pool: PrimaryVolume
 state: ONLINE
  scan: scrub repaired 72K in 0h0m with 0 errors on Fri Nov 24 22:23:20 2017
config:

	   NAME											STATE	 READ WRITE CKSUM
	   PrimaryVolume								   ONLINE	   0	 0	 0
		 raidz3-0									  ONLINE	   0	 0	 0
		   gptid/be639b4e-d1a4-11e7-8e3c-00155d017f10  ONLINE	   0	 0	 0
		   gptid/bf25c58b-d1a4-11e7-8e3c-00155d017f10  ONLINE	   0	 0	 0
		   gptid/bff059ab-d1a4-11e7-8e3c-00155d017f10  ONLINE	   0	 0	 0
		   gptid/c0cbad00-d1a4-11e7-8e3c-00155d017f10  ONLINE	   0	 0	 0
		   gptid/c1a2e809-d1a4-11e7-8e3c-00155d017f10  ONLINE	   0	 0	 0
		   gptid/c269673e-d1a4-11e7-8e3c-00155d017f10  ONLINE	   0	 0	 0
		   gptid/c2eaeb56-d1a4-11e7-8e3c-00155d017f10  ONLINE	   0	 0	 0
		   gptid/c36c0c72-d1a4-11e7-8e3c-00155d017f10  ONLINE	   0	 0	 0

errors: No known data errors

So I was curious how FreeNAS/ZFS behaved if I tried to fill up a Dataset without a quota on pool. I ran the following command on a folder in the dataset and waited:

Code:

cat /dev/urandom > random_data

The results were not good. Here is what I observed:

* The command never terminated. When the pool was full, the command kept running. What was it actually doing? I do not know.
* After rebooting, there were a ton of errors that prevented the Web GUI from starting up. I double checked that I didn't accidentally run this on the system filesystem, and I did not. Tons of messages in syslog about the pool being full though, which is to be expected.
* After deleting the file, the web GUI would start up again on reboot, and the error messages stopped being logged to syslog.

Can someone explain this behavior to me? Also, if it was a remote client via SMB filling up the pool instead of myself on a shell session, what would they expect to see?

 

[joeschmuck]

I think the ZFS question is the type of question would be best asked in the FreeBSD forum or some other ZFS forum for the questions abotu what is ZFS doing. Have you done any Google searches on "freebsd zfs dataset full" or something like that to see if there is any information out there?

Maybe someone here would know why the GUI would act the way it did but I'm betting not many people fill the vdevs.

And now I want to try that command to fill up a dataset but I won't today.