El-Torito and HD partitions

[JamesP]

The MS website and the Sean Liming's XP Embedded Advanced book both
contain the following warning at the end of their El Torito howto:

"You can format the other two partitions on the hard disk and use them
for other purposes, but you cannot repartition the disk in any way
that might cause the offset of any partition to change. Such a change
causes a new boot device identifier to appear in the registry and the
El Torito system continually prompts you to reboot."

Does this mean that I need to keep the partition table of our
production system looking exactly as it did when I constructed the El
Torito bootable CD on our build system?
What if we have systems in the field with different partition sizes,
and layouts, etc. Is it possible to use El Torito? If not, how does
the Win PE CD work? It seems to discover existing partitions just
fine.

Thanks,

James

 

[KM]

JamesP,

The MS website and the Sean Liming's XP Embedded Advanced book both
contain the following warning at the end of their El Torito howto:

"You can format the other two partitions on the hard disk and use them
for other purposes, but you cannot repartition the disk in any way
that might cause the offset of any partition to change. Such a change
causes a new boot device identifier to appear in the registry and the
El Torito system continually prompts you to reboot."

Does this mean that I need to keep the partition table of our
production system looking exactly as it did when I constructed the El
Torito bootable CD on our build system?
What if we have systems in the field with different partition sizes,
and layouts, etc. Is it possible to use El Torito? If not, how does
the Win PE CD work? It seems to discover existing partitions just fine.

On post-FBA image just before you burn it on ElTorito CD you may remove all
the values under [HKLM\SYSTEM\MountedDevices] key except the one which
mounts the disk with ELTO signature to C:.

Only limitation could be in partition size with respect to the system
activation requirements (I mean if your target partition is way too far from
what you specified in TD - you will see the system activation error BSOD).

KM

 

[Slobodan Brcin \(eMVP\)]

Hi James,

Just to add to this.

Even if you remove all entries including C:. It should work since during the boot C: and other letters will be autoassigned.

What if we have systems in the field with different partition sizes, and layouts, etc. Is it possible to use El Torito?

I can't get any sense from this.

Partition size is referred to partition size on El-torito CD that contain XPe. So wherever that you move it, it will work since
partition size does not change on CD at it is same as it was during the FBA and CD creation.

Best regards,
Slobodan

JamesP,

The MS website and the Sean Liming's XP Embedded Advanced book both
contain the following warning at the end of their El Torito howto:

"You can format the other two partitions on the hard disk and use them
for other purposes, but you cannot repartition the disk in any way
that might cause the offset of any partition to change. Such a change
causes a new boot device identifier to appear in the registry and the
El Torito system continually prompts you to reboot."

Does this mean that I need to keep the partition table of our
production system looking exactly as it did when I constructed the El
Torito bootable CD on our build system?
What if we have systems in the field with different partition sizes,
and layouts, etc. Is it possible to use El Torito? If not, how does
the Win PE CD work? It seems to discover existing partitions just fine.

On post-FBA image just before you burn it on ElTorito CD you may remove all
the values under [HKLM\SYSTEM\MountedDevices] key except the one which
mounts the disk with ELTO signature to C:.

Only limitation could be in partition size with respect to the system
activation requirements (I mean if your target partition is way too far from
what you specified in TD - you will see the system activation error BSOD).

KM

 

[KM]

Slobodan,

Hi James,

Just to add to this.

Even if you remove all entries including C:. It should work since during the boot C: and other letters will be autoassigned.

I never tried this. But I guess it would only work if you don't have a HDD in the target device when you boot from El-Torito CD,
right?
Otherwise, HDD (active partition) will probably take precedence and would be assigned with C:\.


Konstantin

What if we have systems in the field with different partition sizes, and layouts, etc. Is it possible to use El Torito?

I can't get any sense from this.

Partition size is referred to partition size on El-torito CD that contain XPe. So wherever that you move it, it will work since
partition size does not change on CD at it is same as it was during the FBA and CD creation.

Best regards,
Slobodan

JamesP,

The MS website and the Sean Liming's XP Embedded Advanced book both
contain the following warning at the end of their El Torito howto:

"You can format the other two partitions on the hard disk and use them
for other purposes, but you cannot repartition the disk in any way
that might cause the offset of any partition to change. Such a change
causes a new boot device identifier to appear in the registry and the
El Torito system continually prompts you to reboot."

Does this mean that I need to keep the partition table of our
production system looking exactly as it did when I constructed the El
Torito bootable CD on our build system?
What if we have systems in the field with different partition sizes,
and layouts, etc. Is it possible to use El Torito? If not, how does
the Win PE CD work? It seems to discover existing partitions just fine.

On post-FBA image just before you burn it on ElTorito CD you may remove all
the values under [HKLM\SYSTEM\MountedDevices] key except the one which
mounts the disk with ELTO signature to C:.

Only limitation could be in partition size with respect to the system
activation requirements (I mean if your target partition is way too far from
what you specified in TD - you will see the system activation error BSOD).

KM

 

[Slobodan Brcin \(eMVP\)]

Konstantin,

I never tried this. But I guess it would only work if you don't have a HDD in the target device when you boot from El-Torito CD,
right?
Otherwise, HDD (active partition) will probably take precedence and would be assigned with C:\.

I have not tried it either, but. To higher level drivers el-torito and HDD are same thing, they are both handled trough disk.sys
driver.
ntldr pass along with ARC names disk id and MBR CRC. Then kernel match this signature with same disk signature calculated trough
disk.sys driver.

From that point forward (this is time before volume letters are assigned) OS knows what partition belong to the OS itself.
So OS partition should take precedence to all other partitions in volume letter assignment algorithm.

This mean that it should be C:, right?

Best regards,
Slobodan

 

[KM]

Slobodan,

Well... You are absolutely right about the disk.sys but (there is always some but's ) according to the
http://support.microsoft.com/default.aspx?scid=kb;en-us;93373:
This process is repeated for all hard drives in the system. Please note that if you have multiple controllers in your system,
the drive letter ordering is based on the order in which the device drivers are loaded by Windows NT.

I assume CD-ROM could sit on a different controller (it is often the case). Would it be primary controller? or secondary? I don't
know. But if it is the secondary one and there is a HDD on primary - HDD would probably take C:\.

Again.. it is up to an experiment.

 

[Slobodan Brcin \(eMVP\)]

Konstantin,

You believe to everything that ms writes?
And this doc is not even for Win XP.

I don't remember that I saw valid document on this topic, but simple experiment is always the best way to see the real behavior.

In our case we have scenario similar to one that I know that work.

Test hardware: 2 HDD's
First have XP.
Second have pre FBA XPe .

We swap in BIOS HDD boot order.
And XPe partition will be given volume letter C: before FBA starts.
Drivers load order is independed of BIOS settings, so this probably mean that link you provided is not accurate for Win XP.

What do you think?

Regards,
Slobodan

 

[KM]

Slobodan,

Even worse.. I sent you NT 3.51 (not even NT 4.0) link :-( For sure rules have changed since the OS version.
Sorry for that link.

Here is an update for XP: http://support.microsoft.com/default.aspx?scid=kb;en-us;825668

Please note this paragraph: "When you install Windows Server 2003 or Windows XP on a computer that has two hard disks, where one
hard disk is configured as master on the primary integrated device electronics (IDE) channel and where the other hard disk is
configured as master on the secondary IDE channel, by default,*** Setup may assign the logical drive C to the hard disk that is
configured as master on the secondary IDE channel. This is a change from the behavior in Windows 2000.,*** When you install Windows
2000 on computer that uses the same hard disk configuration, Windows 2000 Setup tends to assign the logical drive C to the hard disk
that is configured as master on the primary IDE channel".

That's being said that the XP drive letter assignment rules have been changed even since 2K.

So this info just confirms your testing result outlined below.

Also, it means that El-Torito may be seen as C:\ even if it is on secondary IDE channel and there is a HDD on primary. However, only
experiment may answer this.
In one of my test cases, for example, I have CD-ROM on secondary master channel and it is seen as D:. (although it is not a clear
test as I have two HDD's with a few partitions on them).

Thanks for the clarification anyway!

 

[Slobodan Brcin \(eMVP\)]

Konstantin,

Thanks for the link, now I know that I'm not imagining things ;-)

Regarding you D: for CD-ROM.
Unfortunately in your test you have C: allocated already for OS. And all these algorithms are for determining volume letters from
available letter set.
All volume letters are empty only if we manually erase MountedDevices, or before Windows installation or before XPe FBA.

Anyhow we got to the bottom of this and although test is required I'm confident that El-torito can boot with MountedDevices empty.

Regards,
Slobodan