avail size mismatch : zpool list vs zfs list

[Richard Geary]

I've created a 1Tb RAID-1 pool named NASBackup, and enabled dedup & compression. I'm getting confusing numbers for the available size on the pool vs the dataset.

Pool has 209G available, dataset has only 77G available. There is only one dataset in the pool.

Code:

[root@freenas ~]# zpool list NASBackup                                        
NAME        SIZE  ALLOC   FREE  EXPANDSZ   FRAG    CAP  DEDUP  HEALTH  ALTROOT
NASBackup   928G   719G   209G         -    62%    77%  1.26x  ONLINE  /mnt    

[root@freenas ~]# zfs list -o space NASBackup                                  
NAME       AVAIL   USED  USEDSNAP  USEDDS  USEDREFRESERV  USEDCHILD            
NASBackup  77.4G   858G         0     27K              0       858G            

[root@freenas ~]# zfs get "name,available,used,logicalused,compressratio" NASBac
kup 2>&1|less                                                                  
NAME       PROPERTY       VALUE      SOURCE                                    
NASBackup  name           NASBackup  -                                        
NASBackup  available      75.4G      -                                        
NASBackup  used           860G       -                                        
NASBackup  logicalused    844G       -                                        
NASBackup  compressratio  1.12x      -

Some questions :
1) Why is avail 132Gb smaller on the dataset? There's no parity here.
2) Why is the dataset used property larger than the logicalused property, when compression ratio is 1.12?
3) Why is the zpool alloc size 719G when dedup is 1.26x? Wouldn't that would imply 905Gb un-deduped compressed data? (which is smaller than "used" property)

Thanks!

 

[Richard Geary]

I think I've answered my own question. I have a 250Gb zvol inside my dataset, and the fixed size of the zvol is being deducted from the dataset available size.

For a future FreeNAS version, it would be awesome to get a GUI page for examining zpool & zfs size, used size, logicalused, available, and see the effects of compression & dedup

 

[Richard Geary]

I found a must-read blog post on this :
http://nex7.blogspot.com/2013/03/reservation-ref-reservation-explanation.html

I hope this helps others, documentation for how to think about space on zfs is scattered all over the place.

In my case, since I'm only using this backup drive for backup purposes, not direct usage, I simply removed the refreservation for the zvol (zfs set refreservation=none NASBackup/IWindows)

 

[Stux]

I found a must-read blog post on this :
http://nex7.blogspot.com/2013/03/reservation-ref-reservation-explanation.html

I hope this helps others, documentation for how to think about space on zfs is scattered all over the place.

Great link