Dell Storage Manager 2020 R1 Administrator's Guide

Managing NAS Volume Space

FluidFS maintains file metadata in i-node objects. FluidFS i-nodes are 4 KB in size (before metadata replication) and can contain up to 3.5 KB of file data.

When a new virtual volume is created, a portion of it is allocated as i-node area. When a new file is created and there are no free i-nodes left, an additional portion of the volume is allocated to the i-node area. When a file is deleted, however, the i-node is marked as free (to make the allocation of new file i-nodes efficient) rather than returned to the free-space pool.

Free i-nodes are returned to the free-space of a volume only when the ratio between the free-space and the number of free i-nodes becomes very low. When this situation occurs, a special background process is invoked which runs only until the ratio crosses an internal threshold. The process does not run until all free i-nodes are returned to the free-space.

In deployment environments characterized by large amounts of small files, a massive deletion of small files does not fully reflect in the amount of free-space in the volume. For example, if you filled a 100 TB volume with 70 TB of small files (leaving 30 TB free-space) and then deleted 50 TB of them, the amount of free-space would likely not increase much. However, as long as the workload remains small-file oriented, the system reuses the free i-nodes and does not consume from the free-space. Creating some large files requires more space and eventually return a good portion of the free i-nodes to the free space.