FS_STOREBEHIND(1) AFS Command Reference FS_STOREBEHIND(1)NAMEfs_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:
· 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
· 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 ALSOafsd(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 2013-10-09 FS_STOREBEHIND(1)
