Foglight's ZFS disk usage is different from the output of Unix 'df' command (4245011)

On Solaris zones, the ZFS file system Capacity from 'df -h' shows a different value than what Foglight Infrastructure Cartridge (IC) is displaying.

For example, 'df -h' shows 1% but Foglight's %Used is showing 85%.

The Foglight IC agent retrieves metrics about ZFS from the following commands:

1.   zpool list
2.   zfs list
3.   df –g –l

The computation is based on these.  Using 'df -h'is an incorrect way of retrieving the ZFS file system capacity or usage.  For more information, please refer Oracle documentation here.

Example df –g –l output:

/export            (rpool/export      ):       131072 block size           512 frag size
1147797504 total blocks  154027671 free blocks 154027671 available       154027679 total files
154027671 free files     67174404 filesys id
     zfs fstype       0x00000004 flag             255 filename length

Example zfs list output:

How %Used is calculated:

spaceAvailable =  73.4 GB (ZFS list AVAIL) + 9 GB (reservedspace) = 82 GB

spaceUsed = 5.02 GB (ZFS list USED)

totalSpace = total_with_reserve* = 556 GB

*total_without_reserve = 1147797504 (blocks) X 512 (bytes/blocks) = 547 GB
total_with_reserve = 547 GB / ( 1 – 1/64) = 556 GB 
reservedspace = total_with_reserve - total_without_reserve = 9 GB

%Used = spaceUsed / totalSpace * 100
 = 5.02 / 556 * 100 = 1%

%Free = spaceAvailable / totalSpace *100
= 82 / 556 * 100 = 14.75%

In ZFS, the %Used and %Free above does not always equal 100%.