Freezing and thawing a file system

Freezing a file system is a necessary step for obtaining a stable and consistent image of the file system at the volume level. Consistent volume-level file system images can be obtained and used with a file system snapshot tool. The freeze operation flushes all buffers and pages in the file system cache that contain dirty metadata and user data. The operation then suspends any new activity on the file system until the file system is thawed.

The VX_FREEZE ioctl command is used to freeze a file system. Freezing a file system temporarily blocks all I/O operations to a file system and then performs a sync on the file system. When the VX_FREEZE ioctl is issued, all access to the file system is blocked at the system call level. Current operations are completed and the file system is synchronized to disk.

When the file system is frozen, any attempt to use the frozen file system, except for a VX_THAW ioctl command, is blocked until a process executes the VX_THAW ioctl command or the time-out on the freeze expires.