Windows Embedded for HP Thin Clients - Write Filter Best Practices

Overview

The purpose of this white paper is to discuss the best practices and FAQs for using the Enhanced Write Filter (EWF), File-

Based Write Filter (FBWF), and Unified Write Filter (UWF) on HP thin clients running Windows Embedded operating systems.

See the Administrator Guide or Quick Reference Guide for your operating system for more information on basic usage of

write filters on HP thin clients (see For more information).

For more detailed overview and information about the architecture of each write filter, go to the following MSDN pages:

• EWF: http://msdn.microsoft.com/en-US/library/ff793708(v=winembedded.60).aspx

• FBWF: http://msdn.microsoft.com/en-us/library/ff794219(v=winembedded.60).aspx

• UWF: http://msdn.microsoft.com/en-us/library/jj979962(v=winembedded.81).aspx

Caution

HP highly recommends proper write filter usage for standard thin client use cases. Proper usage includes making sure the

write filter is enabled during standard user (non-administrator) operation and is only disabled by administrators temporarily

to make necessary changes and updates to the system. Administrators should re-enable the filter as soon as updates are

completed.

HP further recommends that the Windows Page File feature is never enabled unless the system is configured with a flash

drive of sufficient capacity to support the high volume of writes this feature produces. The use of the Windows Page File

feature with low-capacity drives will result in premature wearing of the drive, decreased performance, and a decrease in the

lifecycle of the thin client.

If your use case requires usage of thin clients in a non-standard manner, please contact HP support to ensure that your thin

client assets are configured properly.

Thin client memory architecture

Like all computer systems, thin clients have both physical storage and RAM. However, the usage of the resources differs

slightly in thin clients.

Physical storage

The physical storage device that contains the operating system and related files is a solid state drive (SSD), also known as a

flash memory module or flash drive. Flash memory is non-volatile, which means that the contents on the drive persist after

every reboot. The advantage of flash drives over hard disk drives (HDDs) is that the read and write speed is much faster on

flash drives due to the lack of moving parts (such as the read/write search arms in an HDD). However, there is a limit to how

many writes can be performed on a flash drive before performance starts to degrade.

Windows is constantly writing to the drive it is installed on, but for the most part, these writes are not of a permanent

nature. Most operating system-related writes are just to store data temporarily until the system needs that information

again, but each time these writes occur they reduce the lifespan of the flash drive. To prevent excessive wear to and prolong

the life of the flash drive, a Windows Embedded operating system uses a section of RAM called the RAMDisk for write data of

a temporary nature (see RAMDisk for more information).

Write data that is not automatically sent to the RAMDisk would normally be written permanently to the flash drive if it

weren’t for the write filter. A write filter prevents permanent writes from being made to the flash drive, which appears as the

C: drive by default on HP thin clients. However, an administrator can configure the write filter to allow permanent writes

under specific circumstances. The exact method to accomplish this depends on which write filter you are using (which in turn

depends on which Windows Embedded operating system you are running). For more information, see the Administrator

Guide or Quick Reference Guide for your operating system.