NAME

nfsiod, biod − The local NFS compatible asynchronous I/O server

SYNOPSIS

nfsiod [ numdaemons ]

DESCRIPTION

The nfsiod daemon runs on an NFS compatible client machine to service asynchronous I/O requests to its server.  The nfsiod daemons improve performance of both NFS reads and writes. Both try to enlist the aid of an idle nfsiod daemon.  If none is available, then the process itself issues the request to the server and waits for the reply. 

The optimum number of nfsiod daemons 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 Digital UNIX server, 7 is a good number of nfsiod daemons for most systems. 

When reading, if the client believes the process is reading a file sequentially, it requests an nfsiod daemon 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 nfsiod daemon and immediately returns to the process.  If the process is writing data faster than the network or server can process, then eventually all the nfsiod daemons 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 Digital 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 nfsiod daemons then 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 nfsiod daemons. 

FILES

/usr/sbin/nfsiod
Specifies the command path

RELATED INFORMATION

Commands: nfsstat(8)

Daemons: async_daemon(2), mountd(8), portmap(8)