wafl.vol.outOfInodes:notice]: file system on Volume xxx is out of inodes

If you receive this error on a NetApp volume, then it is an indication that the volume has a large number of files and that the volume has run out of inodes.

Here is how NetApp defines inodes.
The number of files a volume can contain is determined by how many inodes it has. An inode is a data structure that contains information about files. Volumes have both private and public inodes. Public inodes are used for files that are visible to the user; private inodes are used for files that are used internally by Data ONTAP. You can change only the maximum number of public inodes for a volume. You cannot affect the number of private inodes. 

Data ONTAP automatically sets the maximum number of public inodes for a newly created volume based on the size of the volume: 1 inode per 32 KB of volume size. When the size of a volume is increased, either directly by an administrator or automatically by Data ONTAP through the autosize feature, Data ONTAP also increases (if necessary) the maximum number of public inodes so there is at least 1 inode per 32 KB of volume size, until the volume reaches approximately 1 TB in size. Growing the volume greater than 1 TB in size does not automatically result in more inodes, because Data ONTAP does not automatically create more than 33,554,409 inodes


You can use the command 'maxfiles' to find the inode consumption status.
 filername> maxfiles cifs_vol1
Volume cifs_vol1: maximum number of files is currently 31876690 (31876690 used).


In order to resolve the issue, you can run the command 'maxfiles <volume name> <value>'

For ex:
filername> maxfiles cifs_vol1 40000000

The new maximum number of files will be rounded to 39999990.


 filername> maxfiles cifs_vol1
Volume cifs_vol1: maximum number of files is currently 39999990 (31876690 used).
 

Space reservation in NetApp

Before we discuss space reservation in NetApp, here is a look at the logical representation of aggregate, volume and LUN.





The LUN is created within a volume. There can be more than one LUN within a volume.


















When creating a LUN, you can reserve all the space required for the LUN or let the LUN consume capacity on need basis.

Scenario 1: Create 100GB LUN on 500GB volume with space reserved enabled. This immediately consumes 100GB capacity on the volume.

Scenario 2: Create 100GB LUN on 500GB volume with space reserved disabled. This creates a LUN of 100GB but doesn't consume the capacity on the volume. As data gets written to the LUN, the capacity is consumed.


NOTES:

1) LUN reservation is a property of the LUN and it is persistent across reboots, TO and GB.

2) There is a property on the volume called 'space gaurantee' or 'gaurantee'. When you create LUN with space reservation enabled then you should check the volume gaurantee settings as well. If volume gaurantee is none, then LUN space reservation might not actually work.

3)  LUN space allocation  is a feature that ensure the LUN follows the T10 SCSI standard. This standard requires that LUN remain online even when the LUN is full. If space allocation is disabled, then when the LUN is full (and it cant grow) it goes offline. However, if the space allocation option is enabled, then when the LUN if full (and it cant grow) it remain online. Hosts can read from the LUN but it cant write to the LUN.

4) LUN space allocation also enables storage to reclaim space automatically when the host deletes data.
  https://library.netapp.com/ecmdocs/ECMP1368845/html/GUID-A926B796-9C0D-4935-A84A-D9BF291487A4.html
https://library.netapp.com/ecmdocs/ECMP1368845/html/GUID-93D78975-6911-4EF5-BA4E-80E64B922D09.html