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nfsiod(8) System Manager's Manual nfsiod(8) NAME
nfsiod, biod - The local NFS compatible asynchronous I/O daemon SYNOPSIS
nfsiod [ numthreads ] DESCRIPTION
The nfsiod daemon runs on an NFS compatible client machine and spawns several IO threads to service asynchronous I/O requests to its server. The I/O threads improve performance of both NFS reads and writes. Both try to enlist the aid of an idle I/O thread. If none is available, the process itself issues the request to the server and waits for the reply. The optimum number of I/O threads to run depends on many variables, such as how quickly the client will be writing, how many files will be accessed simultaneously, and the behaviour of the NFS server. For use with a Tru64 UNIX server, 7 is a good number of I/O threads for most systems. When reading, if the client believes the process is reading a file sequentially, it requests an I/O thread to read a block ahead of what the process is currently requesting. If the readahead completes before the process asks for that block, then the subsequent read system call for that data completes immediately and does not have to wait for the NFS request to complete. Read ahead will be triggered again so the read may find that next block available as well. When writing a file, the client takes the process's data, passes the request to an I/O thread and immediately returns to the process. If the process is writing data faster than the network or server can process, then eventually all the I/O threads become busy and the process has to handle a NFS write itself. This means the process has to wait until the server finishes the write. For Tru64 UNIX servers, the NFS block size is 8Kb and UFS tries to cluster I/O 64Kbs at a time. If the client is running with 7 I/O threads, 8 write requests can be in progress at once. This allows the client and server to write data 64Kbs at a time and is the reason for recommending 7 I/O threads. Unlike nfsd, each client thread can use either UDP or TCP. However, if TCP mounts are active, the nfsiod process will time out, close idle TCP connections, and acknowledge any connections closed by the server. The nfsiod process is also responsible for syncing the access time and modify times for special files and named pipes (fifos). Because I/O to these files does not go through the NFS server, NFS clients have to directly update the access time and modify time attributes. The client threads are implemented as kernel threads; they are part of Process ID 0, not the nfsiod process. The ps axml command displays idle I/O threads under PID 0. Idle threads will be waiting on nfsiod_wait. Therefore, if 7 I/O threads are configured, only 1 nfsiod process is displayed in the output from the ps command, although 7 client threads are available to handle NFS requests. FILES
Specifies the command path Specifies the file for logging NFS activity. RELATED INFORMATION
Commands: nfsd(8), nfsstat(8) Daemons: async_daemon(2) delim off nfsiod(8)
