NAS uses IP network, bandwidth and latency issues associated with IP affect NAS performance. Network congestion is one of the most significant sources of latency in a NAS environment. Other factors that affect NAS performance at different levels are:

1. Number of hops: A large number of hops can increase latency becauseIP processing is required at each hop, adding to the delay caused at the router.

2. Authentication with a directory service such as LDAP, Active Directory, or NIS: The authentication service must be available on the network, withadequate bandwidth, and must have enough resources to accommodate the authentication load. Otherwise, a large number of authentication requests are presented to the servers, increasing latency. Authentication adds to latency only when authentication occurs.

3. Retransmission: Link errors, buffer overflows, and flow control mechanisms can result in retransmission. This causes packets that have not reached the specified destination to be resent. Care must be taken when configuring parameters for speed and duplex settings on the network devices and the NAS heads so that they match. Improper configuration may result in errors and retransmission, adding to latency.

4. Over utilized routers and switches: The amount of time that an over-utilized device in a network takes to respond is always more than the response time of an optimally utilized or underutilized device. Network administrators can view vendor-specific statistics to determine the utilization of switches and routers in a network. Additional devices should be added if the current devices are over utilized.

5. File/directory lookup and metadata requests: NAS clients access fileson NAS devices. The processing required before reaching the appropriate file or directory can cause delays. Sometimes a delay is caused by deep directory structures and can be resolved by flattening the directory structure. Poor file system layout and an over utilized disk system can also degrade performance.

6. Over utilized NAS devices: Clients accessing multiple files can cause highutilization levels on a NAS device which can be determined by viewing utilization statistics. High utilization levels can be caused by a poor file system structure or insufficient resources in a storage subsystem.

7. Over utilized clients: The client accessing CIFS or NFS data may alsobe over utilized. An over utilized client requires longer time to process the responses received from the server, increasing latency. Specific performance-monitoring tools are available for various operating systems to help determine the utilization of client resources.

Configuring VLANs and setting proper Maximum Transmission Unit (MTU) and TCP window size can improve NAS performance. Link aggregation and redundant network configurations ensure high availability.