Hi all,

I am moving to Solaris11 and is trying to understand how ZFS snapshot works.

Chances upon this Oracle Blog and can't wrap my head around it.
https://blogs.oracle.com/solaris/understanding-the-space-used-by-zfs-v2

Hope gurus here can shed some light .

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Here it goes,

I understand snapshot works on copy on write mechanism, so if there isn't any changes, there wouldn't be extra space taken.

q1) Why is it that when file1 is deleted, both snap1 and snap2 isn't utilizing any space ?

Code:

bleonard@os200906:~# rm /tank/file1
bleonard@os200906:~# zpool scrub tank
bleonard@os200906:~# zfs list -t all -r tank
NAME         USED  AVAIL  REFER  MOUNTPOINT
tank         200M   784M   100M  /tank
tank@snap1    17K      -   100M  -
tank@snap2    17K      -   200M  -

Yet when using zfs list as below, it is showing that 100M is use by snapshot
(USEDSNAP - 100M)

Code:

 
 bleonard@os200906:~# zfs list -t all -o space -r tank
NAME        AVAIL   USED  USEDSNAP  USEDDS  USEDREFRESERV  USEDCHILD
tank         784M   200M      100M    100M              0       154K

So when file1 is deleted, snap1 and snap2 is not utilizing any space but 100M is used by snapshots ?...

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q2) However, when snap1 is deleted, snap2 will show that it is using 100M of space.. why so ?

Code:

 
 bleonard@os200906:~# zfs destroy tank@snap1
bleonard@os200906:~# zfs list -t all -r tank
NAME         USED  AVAIL  REFER  MOUNTPOINT
tank         200M   784M   100M  /tank
tank@snap2   100M      -   200M  -

I am sure I am looking at this the wrong way...

Regards,
Noob