Windows Embedded for HP Thin Clients - Write Filter Best Practices

Best practices

The following best practices will help ensure a secure and stable environment:

• Keep the write filter enabled when you are not performing necessary configuration.

• Monitor and modify the RAMDisk as necessary (see Memory management for more information).

• When installing large applications, increase the size of the RAMDisk or temporarily change the environment variables TMP

and TEMP to point to C:\Temp (create the folder first, if needed). Be sure to change environmental variables back to

their default settings after installation.

Note

A more detailed procedure might be available in the Administrator Guide for your operating system (see For more

information).

Memory management

For the most part, the easiest RAM partition to manage is the UMA frame buffer. The size can range from 32 MB to 1 GB. The

target size depends on how much video is used in day-to-day operations. If the thin client is used to connect to a remote

session for general office work, then the video buffer can be lower since video operations will not be performed very often.

On the other hand, if there is a lot of video streaming in the remote session, the video memory might need to be increased

because often some of the rendering is left to the client device.

The same is the case with the RAMDisk. For more intense work, even in a remote session, the RAMDisk should be set to a

larger size because there would be more I/O request packets (IRPs). For general office work, a smaller size would fulfill the

need.

In all cases, it would be best to start with the default values and progressively adjust them as needed. Remember that

increasing or decreasing the size of these two partitions has a direct relation to main system memory, which could have an

impact on how many or even the type of programs that the system will be able to run.

As the Write Filter RAM cache memory fills up, the system will start to destabilize. When this happens, random errors can

appear, or the system might even just crash. If possible, HP recommends performing regular maintenance reboots on all

thin clients to clear the Write Filter RAM cache.

There are also certain functions that could have a detrimental effect on the thin client, so these best practices should be

followed to minimize problems:

• Scheduled tasks—Often, in an enterprise environment, there are tasks set to maintain personal systems such as

desktops and notebooks. However, these same tasks can harm the flash drive on the thin client and should not be run.

One example is Disk Defragmenter. Not only would Disk Defragmenter have no real value on an SSD, it would write

directly to disk and shorten the life of the flash drive. Other reoccurring tasks, such as Windows Update and WinSat

should also be avoided so the flash drive is not subjected to excessive writes.

• Image builds

– When building an image, it is best to turn off the write filter and redirect the Temporary Internet Files and TEMP

directories to the C: drive. Often, the RAMDisk does not have enough free space for application installers, so it could

cause various issues during application installation. Building an image in this way avoids these problems and is as close

to building an image in full Windows as possible. Install all necessary applications, make sure that all necessary

reboots are performed (some applications require more than one) and then redirect the Temporary Internet Files and

TEMP directories back to the RAMDisk. Then, turn on the write filter and test the system with the image.

– It is important to make sure that none of the applications installed require, or even attempt to configure, a page file, as

this is not supported.

– When building or cloning an image, do not take up all of the space on the flash drive. A small amount of space should

be left for the EWF volume, which is created by the operating system. 10 MB of space will allow plenty of room for the

volume.