What kind of disk operation is not read or write?

When reading a performance chart like this, what does the Other IO/Sec mean? What kind of operation is not read or write?

The info button only leads to a doc with this vague description:

• NFS Write – When selected, displays NFS write Input/Output operations per second.
• NFS Read – When selected, displays NFS read Input/Output operations per second.
• NFS Other – When selected, displays NFS other Input/Output operations per second.

It depends on what those things are measuring.

It is possible that from a network filesystem perspective traversing a directory does not count as a file read or write operation, or that read or write operations only count on actual disk access and operating system cache hits are not counted. The first read to get a directory listing might hit the disk, but subsequent scans hit the cache in either the OS or the network filesystem stack.

There are also some level of overheads in network "keep this connection alive", "acknowledge" packets and "send me the next one" that could be counted amongst "other" I/O.

There are many other I/O requests to a file-system besides read and write.

Some examples:

• flush : write buffer data to the physical file
• seek : position file to a given offset
• open file
• close file
• resize file
• etc.