Veritas File System 5.0 AdministratorÆs Guide, HP-UX 11i v3, First Edition, May 2008

These advisories are in memory only and do not persist across reboots. Some
advisories are currently maintained on a per-file, not a per-file-descriptor, basis.
Only one set of advisories can be in effect for all accesses to the file. If two
conflicting applications set different advisories, both must use the advisories that
were last set.
All advisories are set using the VX_SETCACHE ioctl command. The current set of
advisories can be obtained with the VX_GETCACHE ioctl command.
See the vxfsio(7) manual page.
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.
Getting the I/O size
VxFS provides the VX_GET_IOPARAMETERS ioctl to get the recommended I/O sizes
to use on a file system. This ioctl can be used by the application to make decisions
about the I/O sizes issued to VxFS for a file or file device.
See the vxtunefs(1M) and vxfsio(7) manual pages.
See “Tuning I/O” on page 44.
65VxFS I/O Overview
Freezing and thawing a file system