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.

Unsigned integer (32-bit)

1

0 to 2³¹ - 1

Asynchronous requests

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.

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.

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.

Unstable

Controls the mix of asynchronous requests that are generated by the NFS version 3 client. There are five types of asynchronous requests, read-ahead, putpage, pageio, readdir-ahead, and commit. 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 3 servers such as write gathering depends upon certain behaviors of existing NFS version 3 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.

Unsigned integer (32-bit)

1

0 to 2³¹ - 1

Asynchronous requests

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.

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.

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.

Unstable

Controls the duration of time that threads, which execute asynchronous I/O requests, sleep with nothing to do before exiting. When there are no more requests to execute, each thread goes to sleep. If no new requests come in before this timer expires, the thread wakes up and exits. If a request does arrive, a thread is woken up to execute requests until there are none again, and then goes back to sleep waiting for another request to arrive, or for the timer to expire.

Integer (32-bit)

6000 (1 minute expressed as 60 sec * 100Hz)

0 to 2³¹ - 1

Hz (Typically, the clock runs at 100Hz)

Yes

None. However, setting this parameter to a non-positive value has the affect of having these threads exit as soon as there are no requests in the queue for them to process.

If the behavior of applications in the system is known precisely and the rate of asynchronous I/O requests can be predicted, it might be possible to tune this parameter to optimize performance slightly in either of the following ways:

• By making the threads expire more quickly, thus freeing up kernel resources more quickly,

• Or, by making them expire more slowly, thus avoiding thread create and destroy overhead.

Evolving

Tunes the number of hash queues that access the file access cache on the NFS client. The file access cache stores file access rights that users have with respect to files that they are trying to access. The cache itself is dynamically allocated, but the hash queues used to index into it are statically allocated. The algorithm assumes that there is one access cache entry per active file and four of these access cache entries per hash bucket. Thus, by default, the value of this parameter is set to the value of the nrnode parameter.

Integer (32-bit)

The default setting of this parameter is 0, which means that the value of nacache should be set to the value of the nrnode parameter.

1 to 2³¹ - 1

Access cache entries

No. This value can only be changed by adding or changing the parameter in the /etc/system file, and then rebooting system.

None. However, setting this parameter to a negative value will probably cause the system to try to allocate a very large set of hash queues, and then hang while trying to do so.

Examine the value of this parameter if the basic assumption of one access cache entry per file would be violated. This might be true for systems in a time sharing mode where multiple users are accessing the same file at about the same time. In this case, it might be helpful to increase the expected size of the access cache so that the hashed access to the cache stays efficient.

Evolving

Controls the duration of time that the NFS version 3 client waits to transmit a new request after receiving the error, NFS3ERR_JUKEBOX, from a previous request. The error, NFS3ERR_JUKEBOX, is generally returned from the server when the file is temporarily unavailable for some reason. These situations are generally associated with hierarchical storage and CD or tape jukeboxes.

Long integer (32 bits on 32-bit platforms and 64 bits on 64-bit platforms)

1000 (10 seconds expressed as 10 sec * 100Hz)

0 to 2³¹ - 1 on 32-bit platforms

0 to 2⁶³ - 1 on 64-bit platforms

Hz (typically the clock runs at 100Hz)

Yes

None

Examine the value of this parameter and perhaps adjust it to match the behaviors exhibited by the server. The value should be increased if the delays in making the file available are long in order to reduce network overhead due to repeated retransmissions. The value can also be decreased to reduce the delay in discovering that the file has become available.

Evolving