The estimated size of the inode list is deducted from the available space reported by df command on Veritas File System (VxFS)

The inodes on a Veritas File System (VxFS) file system are allocated dynamically, so the inode list is not fixed in size and grows dynamically on an as-needed basis.  VxFS takes into account the estimated size of the inode list when the file system available space is reported in the "df -k" output.   The actual available space of a file system is reported by the "df -t" output.

From the df -t command, the actual available filesystem space and the "estimated" total number of inodes in the dynamic inode list are reported by VxFS.

# df -t /mnt        
/mnt        (/dev/vx/dsk/testdg/vol512g):1,073,346,184 blocks 134,168,272 files  
                                         <<<1,073,346,184 is the actual available space in 512-byte blocks
                                         <<<134,168,272 is the estimated number of "free" inodes in the inode list
                   total:1073741824 blocks 134168276 files

The estimated number of free inodes in the dynamic inode list is deduced from the actual available space of the filesystem and the assumption that the average file size of 4KB (or 8 512-byteblocks) for a newly created file system.

Estimated number of free inodes
= Available space of the file system in 512-byte blocks / 4KB (or 8512-byte blocks) for each file
= 1,073,346,184 / 8
=134,168,273

The available space reported by VxFS in the df -k output takes into account the size of these estimated free inodes in the dynamic inode list.

# df -k /mnt
Filesystem            kbytes    used  avail capacity  Mounted on
/dev/vx/dsk/testdg/vol512g
                   536,870,912  197820503,131,031     1%    /mnt

When the total space(kbytes) is subtracted by the available space (avail), the result is not the same as the used space (used).

536870912 - 503131031 = 33739881 which is not the same as 197,820.

There is a difference of 33,739,881 - 197,820 =33,542,061 KB.

This space of about 33 GB is the estimated size of the free inodes.

From the df -t output, we can match this estimated size of the free inodes.

Estimated size of the free inodes
= Estimated number of free inodes from df -t * size of each inode
= 134,168,272 * 256 bytes
=33,542,068 KB  (it is slightly different from 33,542,061 because the actualcalculation is more complicated.)

Customers should use the "df -t"command to obtain the actual available space of a VxFS file system if required.