ZFS volume usage issue

[duwn124]

hi all, I create one zvol in my ZFS volume, and the size of zvol is 6.74TB, the last space is 180GB,just like the picture show.

The zvol is shared through ISCSI. Then i copy many files into the shared zvol. But when the free space still have 2.22TB, I can not write any more file into the shared zvol.

And you can find one CRITICAL error in freeNAS console"CRITICAL:The capacity for the volume 'pacs_ct' is currently at 98%, while the recommended value is below 80%."

Then check the status of ZFS volume. Find that the space which never been shared have gone. as the following picture shows.

That really comfused me. I just shared the zvol and copy files into it. But where is the 180GB have gone. Please help me to analysis this issue. Any help and comment is welcomed. Thanks a lot for any helps.

 

[dlavigne]

What is the size of the zvol? The warning is telling you that it is a bad idea to use over 80% of the pool's capacity for a zvol.

 

[duwn124]

What is the size of the zvol? The warning is telling you that it is a bad idea to use over 80% of the pool's capacity for a zvol.

Assigned 6.74TB and used 4.51TB(almost 67%usage). I can't write any more data into the zvol. I don't know what data have been writen into the space(180GB) left in ZFS volume. In my mind, the 180GB should never been used since it have not be shared and i never write any data yet.

 

[rs225]

The ZVOL was probably created with too small block size and/or compression is not on. Start over again with a new ZVOL that has larger block size when you create it.

 

[duwn124]

The ZVOL was probably created with too small block size and/or compression is not on. Start over again with a new ZVOL that has larger block size when you create it.

The zvol is created with the default block size 8Kbytes. And there still have two problems:
1. Which block size is recommend? I have more than 50 millions files need to write into the zvol.
2.I just write data into the zvol, but why the left capacity in the ZFS pool(180GB) have been used up? What data have been writen into the left capacity?
Thanks a lot!

 

[rs225]

I would go with a 32KiB block size. You might also try formatting the NTFS as 32KiB cluster, but test to make sure it still works correctly with your files and programs.

Do not worry about the 180GB; worry about the 2TiB that has been wasted. If you used up all the free space, it would be very bad. ZFS must have free space.

 

[duwn124]

Thanks for all helps.
I have recreate zvol with 64k block size and it seems work well.

Here is another post maybe help.
https://bugs.freenas.org/issues/2383

But if anyone could tell me why samll block size will comsume more capacity? Thanks.

 

[mav@]

What is your pool configuration? If it is RAIDZx, then for every block written (however small it is) ZFS also writes x*4K of cheksum data.

 

[jgreco]

And for a zvol or other block storage, if it is going to sustain active write activity, that 80% warning is far too high... you should make sure you're not filling your pool to more than maybe 60% or even 40-50% if you want a good chance at keeping performance acceptable.