File system development

Question

When designing a file system that uses an inode structure to point to files / blocks, what is the number of actual inode definitions?

Answer 1

On some Unix file systems (for example, ext * fs) that actually correspond to the system administrator who sets the relative parameter when creating the file system.

If the file system will contain many small files (a typical example is news and mail servers), you need a large number of inodes, since for each object (file or directory) you need an inode.

If, on the other hand, the file system will host larger files (for example, a video server), you do not need so many inodes.

Since inodes take up space, it is important to strike a balance between efficiency and effectiveness and have enough descriptors for your purpose. A simple method is to calculate the average file size in an active file system with similar usage patterns and use this number as the base value for the byte / index ratio on the new FS. This would allow FS to function while the volume is being filled, until usage patterns change dramatically.

If you are actually developing a new file system, and not just creating a volume, you should consider the idea of ​​dynamically allocating inodes dynamically, like some other common Unix file systems (e.g. JFS, XFS, Reiserfs). This would make your file system a little more flexible, although it is generally believed that the FS dynamic structures greatly complicate the recovery process due to corruption issues.

Answer 2

Some modern file systems (XFS for one) allocate inodes dynamically as needed. File systems without this function select an experiential value relative to disk size (for example, ext2 / 3/4 creates 1 inode per 4KB IIRC disk space), and there is usually a way to adjust this value when creating a file system.