nfs:nfs_async_clusters

Description

Controls the mix of asynchronous requests that are generated by the NFS version 2 client. There are four types of asynchronous requests, read-ahead, putpage, pageio, and readdir-ahead. The client attempts to round-robin between these different request types to attempt to be fair and not starve one operation type in favor of another.

However, functionality in some NFS version 2 servers such as write gathering depends upon certain behaviors of existing NFS Version 2 clients. In particular, this functionality depends upon the client sending out multiple WRITE requests at approximately the same time. If one request is taken out of the queue at a time, the client would be defeating this server functionality designed to enhance performance for the client.

Thus, use this parameter to control the number of requests of each type that are sent out before changing types.

Data Type

Unsigned integer (32–bit)

Default

1

Range

0 to 2³¹ - 1

Units

Asynchronous requests

Dynamic?

Yes, but the cluster setting for a file system is set when the file system is mounted. To affect a particular file system, unmount and mount the file system after changing this parameter.

Validation

None. However, setting the value of this parameter to 0 causes all of the queued requests of a particular type to be processed before moving on to the next type. This effectively disables the fairness portion of the algorithm.

When to Change

Change this parameter to increase the number of each type of asynchronous operation that is generated before switching to the next type. This might help with server functionality that depends upon clusters of operations coming from the client.

Stability Level

Unstable