SUMMARY:

To protect partitions on a removable media such as compact flash cards you can use the Enhanced Write Filter feature. For instance, you may want to protect any changes in the operating system image. This article elaborates on how to set Enhanced Write Filter on a removable media and after that lists few of the problems that you might experience.

MORE INFORMATION:

Compact flash cards are reported to the operating system as removable media if the creator supplies a tool which you can use to convert the compact flash cards to Un-detachable media.

• Detachable. You need to follow step 2 ( as shown in the later section) just for detachable compact flash cards.

• Un-Detachable. For Un-Detachable compact flash cards, you can directly copy the pre-FBA image on the compact flash card and let FBA run on its own (and same with the hard disks).

Before making, confirm that you set following correctly in Target Designer:

a. Make sure that the Enhanced Write Filter components are included and that its settings are set accordingly. Amongst these settings, run Enhanced Write Filter Enabled check box, and after that confirm that the Enhanced Write Filter Partition Size in Kb’s field in the Enhanced Write Filter component is set to a correct value. For RAM-based overlays, 32 KB or larger is sufficient.

b. You do not need to include the El Torito component in the design, neither required to use the Etprep.exe tool (see step 2).

c. Enter a value in the Boot Partition Size field in Target Device Settings of the root node. This value is the size of the compact flash boot partition (for instance 300MB)

Follow these steps to set Enhanced Write Filter on Compact flash cards:

a. Apply a different disk drive (for instance, disk drive A) to hold the temporary image which you later copy to the Compact flash card. In other way, use a separate drive from the main drive on your computer.

b. Confirm that the drive A has a primary partition (which is having sufficient space to hold the embedded operating system image) and has raw space for the Enhanced Write Filte partition to be made (as prescribed by the Enhanced Write Filte Partition Size in KB’s field in the Enhanced Write Filte properties). Remove any existing Enhanced Write Filte partitions (reported as non-dos partition in Fdisk.exe).

c. Plug up the drive A into the development computer.

d. On development computer, make the design, and after that copy the image to drive.

e. Move drive A to the target boot computer to drive A, and then let FBA run until it finishes.

f. Confirm whether the Enhanced Write Filte was set up properly on the target runtime on drive A: after that you log on, run the following command and after that look at the output for any errors: type
ewfmgr c:

g. Shift drives A and the Compact flash card to the development computer, and after that copy the post-FBA image from drive A to the Compact flash card.

Confirm that the Compact flash card was already set up, that is, partitioned (by using Fdisk.exe), formatted ( by using Format.exe), and "bootprep'd" to make it bootable in XP.

h. Shift the Compact flash card to the main master integrated development environment channel on the target computer and after that run the system from the Compact flash card.

Issues When Using Enhanced Write Filte on Removable Media

When using Enhanced Write Filter you may come across the following issues on detachable (removable) media:

The FBA log may indicate an error while making or starting the Enhanced Write Filte partition.

If you enter ewfmgr in the runtime, the following message will come on your screen.
Incapable to find Enhanced Write Filte partition.

When you enter ewfmgr c: to verify the status of the protected volume, everything looks well except for the next boot command. This boot command line is not in the output and there is no way to find out the next boot command.

Enabling or disabling RAM-based Enhanced Write Filter is supported only in Enhanced Write Filter SP1 version. Though to disable Enhanced Write Filter, you should also commit as part of the disabling process. A commit is needed to wash out the disable registry key to disk so that the Enhanced Write Filter can be familiar with it the next time so that the computer starts.

Follow these steps to disable RAM-based Enhanced Write Filter on SP1 systems:

a. Run ewfmgr c: -disable command.

b. Run ewfmgr c: -commit command.

c. Then start your computer again.
When to Use the EtPrep Tool

d. If you are not using the hard disk (drive A) after that the FBA ran on your target Operating System (i.e., as a secondary storage media or to hold the paging file), you do not have to change drive letters. Hence, you also do not require Etprep.

e. In this instance, after the computer starts it finds that the Compact flash card is the only available volume on your system, after that the system assigns the Compact flash card to another drive i.e. drive C, even though this letter was found on the hard disk previously. This drive assignment arrives because the hard disk volume is no longer in existence. Hence, drive C is re-directed to the Compact flash card and the Compact flash card starts to works well.

If you continue to use the same hard disk on your computer and the system cannot direct drive C to the Compact flash card if you do not explicitly changes the drive letters. You cannot run your computer from the Compact flash drive. Reason the image was made for drive C.
Enhanced Write Filter may work well regardless of these problems. To check Enhanced Write Filter, followthese steps:

1. Allow Enhanced Write Filter: run the ewfmgr c: -enable command.

2. Then start your computer again.

3. Make changes in the Operating System image.

4. Then start your computer again.

5. Confirm that the changes that you made in step 3 do not carry on.