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freezefs(2)
NAME
freezefs - The freezefs() API causes the specified fileset's domain to
enter into a metadata stable state, causes a previously frozen fileset's
domain to resume normal activity, or queries the freeze state of the
fileset's domain. All the filesets in the AdvFS domain are affected.
SYNOPSIS
#include <sys/mount.h>
int freezefs {
char *mountPoint,
u_long optionFlags,
int timeout };
);
PARAMETERS
mountPoint
Points to a null-terminated string that contains the appropriate mount
point of the file system.
optionFlags
Specifies what action to take on the specified file system.
FS_Q_QUERY
Queries the freeze state and indicates whether or not the domain is
frozen by way of the return code.
FS_Q_FREEZE
Places the filesystem in a metadata consistent state and guarantees
that it stays that way until thawed. All metadata, which could be
spread across multiple volumes or logical units (LUNS), is flushed
to disk and does not change for the duration of the freeze.
FS_Q_THAW
Causes a previously frozen fileset's domain to resume normal
activity.
timeout
Specifies the maximum time allowed for the fileset's domain to
remain frozen:
> 0
Specifies the timeout value in seconds.
= 0
Uses the default timeout specified in the vfs stanza of
/etc/sysconfigtab as freezefs_default_timeout. If not specified in
/etc/sysconfigtab, freezefs uses 60 seconds.
< 0
Specifies no timeout. The fileset's domain remains frozen until
explicitly thawed.
Certain system events on a cluster will cause automatic thaws regardless of
timeout value. See DESCRIPTION for more information.
DESCRIPTION
To allow coherent hardware snapshots in multivolume domain configurations,
filesystem metadata must be consistent across all volumes when the
individual volumes are snapped or cloned. These configurations include
both multivolume AdvFS domains and multivolume LSM logical volumes.
The FS_Q_FREEZE option to the freezefs API places the filesystem in a
metadata-consistent state and guarantees that it stays that way until
thawed. All metadata, which could be spread across multiple volumes or
logical units (LUNs), is flushed to disk and does not change for the
duration of the freeze.
The filesystem thaws either by timing out or explicitly with the FS_Q_THAW
option to the freezefs() API. If you are running a cluster configuration,
shutting down any node or the failure of any node will also thaw the
filesystem.
The exact nature of the freezefs API depends on whether you are running on
a single system or a cluster.
Single System
When you freeze a filesystem, any in-process metadata updates are allowed
to finish. Filesystem operations that do not modify metadata are allowed
while frozen. Some operations will work normally even if the target
fileset's domain is frozen, for example:
· Read
· No-extending write
· Stat
Filesystem operations that modify metadata are blocked. The following
operations will block if the target fileset's domain is frozen, for
example:
· Mount of fileset
· rmvol
· Extending write
· mkfset / rmfset
The following filesystem operations will fail immediately if the target
filesystem (that is, domain) is frozen:
· Mount update of fileset
· Unmount of fileset
Cluster
When you freeze a filesystem in a clustered configuration, all in-process
filesystem operations are allowed to complete. Some filesystem operations
are allowed while frozen. The following operations, which do not require
metadata updates, will work normally even if the target filesystem is
frozen.
· Read
· Stat
Most new filesystem operations are blocked when the filesystem is frozen.
Operations that have the potential for requiring metadata updates will
block if the target filesystem is frozen, for example:
· Write
· chmod
· Link
Some filesystem operations will fail immediately if the target domain is
frozen, for example:
· Unmount of fileset
· Mount (update) of fileset
· User-initiated planned relocation
· User-initiated forced unmount
· addvol
· rmvol
The freezefs() API posts an event manager (EVM) event when a file system is
frozen or thawed. Use the evmwatch and evmshow commands to determine if any
file systems in the cluster are frozen. See EXAMPLES.
NOTES
At present, freezefs and thawfs functionality is only implemented for AdvFS
filesystems.
Using the freezefs() API for a single mount point affects all filesets in
the domain.
In a cluster configuration, some system events may cause an automatic thaw
regardless of the timeout option. See the DESCRIPTION section for more
information.
RESTRICTIONS
You must be root user to run freezefs and thawfs. The /, /usr and /var
file systems cannot be frozen.
EXIT STATUS
0 (Zero)
Success FS_Q_FREEZE and FS_Q_THAW
Not frozen FS_Q_QUERY
> 0 Frozen FS_Q_QUERY
< 0 An error occurred.
ERRORS
[ENOTSUP]
The freezefs is not supported by the filesystem specified.
[NOENT]
The filesystem is not mounted.
[ENOMEM]
Not enough memory.
[EALREADY]
The file system is already frozen freezefs, or
The file system is not frozen thawfs.
[EPERM]
The caller does not have root privilege.
[EOPNOTSUPP]
Option not supported.
EXAMPLES
1. To freeze a file system:
#include
extern errno;
...
char *mp;
u_long flags;
int timeout, rc;
...
mp = "/oracle"; /* filesystem to freeze */
flags = FS_Q_FREEZE; /* freeze flag */
timeout = 0; /* use default timeout */
...
errno = 0;
rc = freezefs(mp, flags, timeout);
if (rc = -1) {
error
}
.
.
.
PERFORM WORK ON FROZEN FILE SYSTEM
.
.
.
flags = FS_Q_THAW; /* thaw flag */
errno = 0;
rc = freezefs(mp, flags, timeout);
if (rc = -1) { /* If error on thaw, cannot rely on the intial freeze */
error
}
SEE ALSO
Commands: freezefs(8), thawfs(8)
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