Windows Embedded Standard 7 for HP Thin Clients - Administrator Guide

A Enhanced Write Filter and File-Based Write
Filter
IMPORTANT: If your thin client has HP Write Manager, see the administrator guide for HP Write Manager for
instructions. This appendix applies only to thin clients that do not have HP Write Manager.
A write lter protects the contents of and decreases wear on the ash drive of a thin client by redirecting and
caching writes in an overlay. An overlay is a virtual storage space in RAM that tracks changes to a protected
volume (the ash drive). The user experience in Windows is unaected because the operating system
maintains the appearance of writing to the ash drive. When a system restart occurs, the overlay cache is
cleared, and any changes made since the last system startup are lost permanently. If it is necessary to make
permanent system congurations, an administrator can commit (persist by writing through to the protected
volume) changes stored in the overlay cache prior to a system restart.
NOTE: The overlay cache is cleared only by a system restart, so users can log out or switch between user
accounts without losing the cached information.
You can choose between the following write lters:
● Enhanced Write Filter (EWF)—EWF allows you to commit the entire overlay cache in a single command.
However, you cannot manage on a per-le basis, so you cannot commit les individually, restore les to
their previous state from the underlying volume (unless you clear the entire overlay cache by restarting
the system), or exclude les from protection.
NOTE: EWF is enabled by default. The EWF commit command requires a system restart.
● File-Based Write Filter (FBWF)—FBWF allows you to manage on a per-le basis, so you can
immediately (without a system restart) commit les individually or restore les to their previous state
from the underlying volume by discarding the changes. You can also exclude les from protection so
that changes to them are always written directly to the ash drive. However, you cannot commit the
entire FBWF overlay cache in a single command.
NOTE: You cannot restore a le after it is committed or after the FBWF overlay cache is cleared. Any
modication to the exclusion list requires a system restart.
CAUTION: HP highly recommends the following:
● Ensure that the write lter is used properly for standard thin client use cases. Proper usage includes
making sure the write lter is enabled during end-user (non-administrator) operation and is disabled
only temporarily by an administrator needing to make changes to the system. The write lter should be
re-enabled as soon as the changes are completed.
● Never enable the Windows Page File feature.
● For use cases that require frequent writes, such as active system logging, call center phone and video
recording, and industrial logging, you should congure the thin client to write to a server. If local writes
are necessary, they should be done in the overlay cache. Please contact HP for help determining an
appropriate interval schedule for committing the overlay cache, or preferably log the data from the
overlay cache to a server.
If your use case requires non-standard write lter usage, please contact HP to ensure that your thin clients
are congured properly.
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