EWF disk overlay on a different hard disk.

  • Thread starter Thread starter jeonghee.kim
  • Start date Start date
J

jeonghee.kim

Hi,

We have designed a hardware appliance which has a CF card and hard disk
drive.
The CF will store the operating systems and the hdd will be used to log
history.

We want to make the one of the hard disk partition as the overlay for
the CF. Is this possible? If so, how can we choose the overlay
partition on the disk?

Thank you.

Jeong
 
It is possible. The hard drive must have at least one partition on the disk
and enough free space (8MB) for EWF to create the EWF Volume during FBA.
During FBA, EWFDLL.DLL will hunt for free space to create the EWF Volume.
Windows XP Embedded Advanced - Chapter 19 - 19.3.4 and 19.3.5 describe this
scenario.

Regards,

Sean Liming
www.sjjmicro.com / www.seanliming.com
XP Embedded Book Author - XP Embedded Advanced, XP Embedded Supplemental
Toolkit
 
Sean: I'm not familiar with any cases where the EWF volume can exist on a
device other than the boot device. In this scenario, I think the user would
need to boot from the hard drive in order for the EWF volume to exist on
that drive - the OS itself can reside on a different device, however.
Basically, NTLDR, NTDETECT.com and boot.ini would exist on the HDD active
partition, and boot.ini would point to the CF device for the OS, so the HDD
would serve as the boot partition and the CF as the system partition.

But to my knowledge, it is not supported (or possible) to have the EWF
volume/overlay exist on a non-boot device. If you've found this to be
possible, I'd be interested in seeing the steps as well.
 
Matt,

Like I mentioned in a similiar post, this was true for SP1, which is why it
is writen in the book. I spent many hours going over this. When I asked if
what I was seeing was correct, I was told yes. If something has changed
between then and FP2007, I will have to go back and look.

Regards,

Sean
 
Sounds like a case where I was misinformed, then - sorry about the
confusion. :)
 
Well, something could have changed. No one has indicated otherwise.

Regards,

Sean
 
Thank you for your answer.
Is that possible to upgrade the CF card without changing anything on
the disk?
One of the reason why we use the CF card plus hard disk is to upgrade
the system easily just replacing the CF card.

My concern is that the overlay partition exists on the disk and there
may be a mismatch between the upgraded software on the CF card and
overlay on the disk.

Best regards,

Jeong
 
That will be a problem. The EWF volume will be a miss match. EWF with
RAM-REG is better suited for upgradability. You may want to consider FP2007
and the File Base Write Filter, which will allow for writes through the
filter and the ability to commit changes to files already on the disk.

What is the reasopn for using the Disk Overlay?

Regards,

Sean Liming
www.sjjmicro.com / www.seanliming.com
XP Embedded Book Author - XP Embedded Advanced, XP Embedded Supplemental
Toolkit
 
Sean,

Our system has a feature that users can upload and install their own
TrueType fonts. For this reason, we need enough space for the fonts. If
we can install the fonts on separate disk rather than the Windows Fonts
directory, we do not need to use the Disk Overlay.

Best regards,

Jeong Kim
ePapyrus, Inc.

PS. I have bought your book which was very helpful to me. It is an
honor to talk with the author.
 
I think FBWF will solve the problem. FBWF will allow you to open a
write-through section for the fonts directory. The question is the timing of
your project and the release of FP2007. There is a tech preview available
for FP2007 that you might want to check out.

Regards,

Sean Liming
www.sjjmicro.com / www.seanliming.com
XP Embedded Book Author - XP Embedded Advanced, XP Embedded Supplemental
Toolkit
 
I was confused about this as well, especially when it says in the XPe help
that this disk based EWF must be on the boot volume:

"EWF Disk mode requires unpartitioned space on the same disk that contains
the protected volume. "

I think Sean went "under the hood" and figured out how to make it work.
This is a nice scenario, as it would allow someone to store prior CF
versions as disk layers. That makes it trivial to back up to an earlier
software release. Nice.
 
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