FS_STOREBEHIND(1)					       AFS Command Reference						 FS_STOREBEHIND(1)

NAME

       fs_storebehind - Enables asynchronous writes to the file server

SYNOPSIS

       fs storebehind [-kbytes <asynchrony for specified names>]
	   [-files <specific pathnames>+]
	   [-allfiles <new default (KB)>] [-verbose] [-help]

       fs st [-k <asynchrony for specified names>]
	   [-f <specific pathnames>+]
	   [-a <new default (KB)>] [-v] [-h]

DESCRIPTION

       The fs storebehind command enables the Cache Manager to perform a delayed asynchronous write to the File Server when an application closes
       a file. By default, the Cache Manager writes all data to the File Server immediately and synchronously when an application program closes a
       file -- that is, the close() system call does not return until the Cache Manager has actually transferred the final chunk of the file to
       the File Server. This command specifies the number of kilobytes of a file that can still remain to be written to the File Server when the
       Cache Manager returns control to the application. It is useful if users working on the machine commonly work with very large files, but
       also introduces the complications discussed in the CAUTIONS.

       Set either or both of the following in a single command:

       o   To set a value that applies to all AFS files manipulated by applications running on the machine, use the -allfiles argument. This value
	   is termed the default store asynchrony for the machine, and persists until the machine reboots. If it is not set, the default value is
	   zero, indicating that the Cache Manager performs synchronous writes.

	   As an example, the following setting means that when an application closes a file, the Cache Manager can return control to the
	   application as soon as no more than 10 kilobytes of the file remain to be written to the File Server.

	      -allfiles 10

       o   To set a value that applies to one or more individual files, and overrides the value of the -allfiles argument for them, combine the
	   -kbytes and -files arguments. The setting persists as long as there is an entry for the file in the kernel table that the Cache Manager
	   uses to track certain information about files. In general, such an entry persists at least until an application closes the file or
	   exits, but the Cache Manager is free to recycle the entry if the file is inactive and it needs to free up slots in the table. To
	   increase the certainty that there is an entry for the file in the table, issue the fs storebehind command shortly before closing the
	   file.

	   As an example, the following setting means that when an application closes either of the files bigfile and biggerfile, the Cache
	   Manager can return control to the application as soon as no more than a megabyte of the file remains to be written to the File Server.

	      -kbytes 1024 -files bigfile biggerfile

	   Note that once an explicit value has been set for a file, the only way to make it subject to the default store asynchrony once again is
	   to set -kbytes to that value. In other words, there is no combination of arguments that automatically makes a file subject to the
	   default store asynchrony once another value has been set for the file.

       To display the settings that currently apply to individual files or to all files, provide the command's arguments in certain combinations
       as specified in OUTPUT.

CAUTIONS

       For the following reasons, use of this command is not recommended in most cases.

       In normal circumstances, an asynchronous setting results in the Cache Manager returning control to applications earlier than it otherwise
       does, but this is not guaranteed.

       If a delayed write fails, there is no way to notify the application, since the close() system call has already returned with a code
       indicating success.

       Writing asynchronously increases the possibility that the user will not notice if a write operation makes the volume that houses the file
       exceed its quota. As always, the portion of the file that exceeds the volume's quota is lost, which prompts a message such as the
       following:

	  No space left on device

       To avoid losing data, it is advisable to verify that the volume housing the file has space available for the amount of data anticipated to
       be written.

OPTIONS

       -kbytes <asynchrony for specified names>
	   Specifies the number of kilobytes of data from each file named by the -files argument that can remain to be written to the file server
	   when the Cache Manager returns control to an application program that closed the file. The -files argument is required along with this
	   argument. Provide an integer from the range 0 (which reinstates the Cache Manager's default behavior or writing synchronously) to the
	   maximum AFS file size.

       -files <specific pathnames>+
	   Names each file to which the value set with the -kbytes argument applies. The setting persists as long as there is an entry for the
	   file in the kernel table that the Cache Manager uses to track certain information about files. Because closing a file generally erases
	   the entry, when reopening a file the only way to guarantee that the setting still applies is to reissue the command. If this argument
	   is provided without the -kbytes argument, the command reports the current setting for the specified files, and the default store
	   asynchrony.

       -allfiles <new default (KB)>
	   Sets the default store asynchrony for the local machine, which is the number of kilobytes of data that can remain to be written to the
	   file server when the Cache Manager returns control to the application program that closed a file. The value applies to all AFS files
	   manipulated by applications running on the machine, except those for which settings have been made with the -kbytes and -files
	   arguments. Provide an integer from the range 0 (which indicates the default of synchronous writes) to the maximum AFS file size.

       -verbose
	   Produces output confirming the settings made with the accompanying -kbytes and -files arguments, the -allfiles argument, or all three.
	   If provided by itself, reports the current default store asynchrony.

       -help
	   Prints the online help for this command. All other valid options are ignored.

OUTPUT

       If none of the command's options are included, or if only the -verbose flag is included, the following message reports the default store
       asynchrony (the setting that applies to all files manipulated by applications running on the local machine and for which not more specific
       asynchrony is set).

	  Default store asynchrony is <x> kbytes.

       A value of 0 (zero) indicates synchronous writes and is the default if no one has included the -allfiles argument on this command since the
       machine last rebooted.

       If the -files argument is provided without the -kbytes argument, the output reports the value that applies to each specified file along
       with the default store asynchrony. If a particular value has previously been set for a file, the following message reports it:

	  Will store up to <y> kbytes of <file> asynchronously.
	  Default store asynchrony is <x> kbytes.

       If the default store asynchrony applies to a file because no explicit -kbytes value has been set for it, the message is instead as follows:

	  Will store <file> according to default.
	  Default store asynchrony is <x> kbytes.

       If the -verbose flag is combined with arguments that set values (-files and -kbytes, or -allfiles, or all three), there is a message that
       confirms immediately that the setting has taken effect. When included without other arguments or flags, the -verbose flag reports the
       default store asynchrony only.

EXAMPLES

       The following command enables the Cache Manager to return control to the application program that closed the file test.data when 100
       kilobytes still remain to be written to the File Server. The -verbose flag produces output that confirms the new setting, and that the
       default store asynchrony is zero.

	  % fs storebehind -kbytes 100 -files test.data -verbose
	  Will store up to 100 kbytes of test.data asynchronously.
	  Default store asynchrony is 0 kbytes.

PRIVILEGE REQUIRED

       To include the -allfiles argument, the issuer must be logged in as the local superuser "root".

       To include the -kbytes and -files arguments, the issuer must either be logged in as the local superuser "root" or have the "w" (write)
       permission on the ACL of each file's directory.

       To view the current settings (by including no arguments, the -file argument alone, or the -verbose argument alone), no privilege is
       required.

SEE ALSO

       afsd(8)

COPYRIGHT

       IBM Corporation 2000. <http://www.ibm.com/> All Rights Reserved.

       This documentation is covered by the IBM Public License Version 1.0.  It was converted from HTML to POD by software written by Chas
       Williams and Russ Allbery, based on work by Alf Wachsmann and Elizabeth Cassell.

OpenAFS 							    2012-03-26							 FS_STOREBEHIND(1)