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What is an inode?

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What is an inode?

An inode is a data structure that defines a file, except for the filename which is stored in the directory entry. Note that a directory is just another file. The inode number is an integer unique to the volume upon which it is stored. inodes point to blocks that make up a file, and inodes also contain the metadata of the file.

When a program refers to a file by name, the system looks up the filename in the directory entry file of the directory in which the file exists to get the proper inode. This gives the system the information it needs about the file to perform further operations.

Each inode contains the following information:

  • Volume where the inode resides
  • Locking information
  • Mode and type of file
  • Number of links to the file
  • Owner's user and group ids
  • Number of bytes in the file
  • Access and modification times
  • Time the inode itself was last modified
  • Addresses of the file's blocks on disk
  • Permission: UNIX bits or Windows Access Control List (ACLs)
  • Qtree ID

Data ONTAP allocates one inode per 32KB of data in a volume by default. This value can be increased to as high as 1 inode per 4KB of data via the maxfiles command.



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