Windows 8 and 8.1 Forums


Booting with multipart vhd possible?

  1. #1


    Posts : 5
    Win8

    Booting with multipart vhd possible?


    I have Windows 8 CP running off a USB stick as a vhd. For the past 24 hours I have been trying to boot a multipart version of that vhd to get the whole setup on a FAT32 formatted stick. Splitting is no problem and is supposedly supported by Virtual Machine emulators, but is it also supported by Win8's boot manager on a real system? Right now,it doesn't look like it.

    If I replace the vhd with the multipart version, then the boot entry just vanishes. Adding it manually with easybcd results in the same thing. I tried to create a vhd on the FAT32 drive during installation in the hopes that it would result in multipart vhd-files automatically, but diskpart errors out due to the 4GB file size limitation. I doubt that this is even supported, but may be someone already did it, or knows a workaround.

    Edit: The post was moved to the virtualization forum. This isn't about running Win8 in a VM though, but booting it on a real system.
    Last edited by Mexxi; 31 Jul 2012 at 09:39.

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  2. #2


    Orbiting the Moon
    Posts : 2,975
    Windows 10 x64


    Well welcome to the virtualization forum anyway .

    I have a To Go USB version. never tried the VHD technique on USB.

    You say it works with the one piece VHD right? But is it running on ntfs partition? Since this VHD can grow very big, it should go on an NTFS partition.

    Even a To Go USB stick (Windows 8 To Go - Setup on a USB Flash Drive or USB Disk) it's formatted in NTFS and as we know, the bootoader of Win7 / Win8 supports NTFS and no fat32.

    So I think it's fat32 the issue of not being able to boot the multipart VHD. Try this multipart on NTFS and if it works: you know it was a fat32 issue.

    Cheers
    Hopachi
      My System SpecsSystem Spec

  3. #3


    Posts : 5
    Win8


    Quote Originally Posted by Hopachi View Post
    Well welcome to the virtualization forum anyway .
    Thank you

    Quote Originally Posted by Hopachi View Post
    You say it works with the one piece VHD right? But is it running on ntfs partition?
    Indeed, it does work and it is stored on an NTFS partition.


    Quote Originally Posted by Hopachi View Post
    Since this VHD can grow very big, it should go on an NTFS partition.
    That's no problem, since vhd-files can be split into many chunks and are loaded as single file. At least VM-software automatically splits them like that (if configured to do so). Since MS announced it would support booting vhd-files, I kinda expected also support for split vhd's. The beauty of that is, that you can have an NTFS based operating system on a FAT32 drive.

    Quote Originally Posted by Hopachi View Post
    Even a To Go USB stick (Windows 8 To Go - Setup on a USB Flash Drive or USB Disk) it's formatted in NTFS and as we know, the bootoader of Win7 / Win8 supports NTFS and no fat32.
    That's alright for a dedicated stick. However, I forked out a pretty penny for one of the fastest 64GB sticks on the market and I don't want to limit its usage to a beta operating system. I have plenty of other devices around that want to benefit from the size and speed of that stick

    I actually repartitioned the stick to an NTFS and a FAT32 partition, but since the second partition isn't recognized by Windows, I had to install filter drivers on all my systems just to circumvent that problem. Still, that doesn't help me for machines I don't own, so using multipart vhd-files seemed like a good alternative.

    Quote Originally Posted by Hopachi View Post
    So I think it's fat32 the issue of not being able to boot the multipart VHD. Try this multipart on NTFS and if it works: you know it was a fat32 issue.
    I wouldn't jump to conclusions so quickly. For one, the boot manager processes the BCD even if it's run off a FAT32 formatted drive. If it wouldn't support FAT32 it would error out before even getting there. Also, it supports XP which runs on FAT32 and Win8 supports upgrades from XP. I really doubt MS forces people to switch over to NTFS.

    All speculation aside, it's easy enough to test FAT32 compatibility. I have a vlited Win 7 that hovers around the 4GB mark. Should be no problem to boot it as a vhd with the Win8 boot manager from a FAT32 drive.

    I rather think that MS merely doesn't support loading multipart vhds. FAT32 shouldn't really matter. I'm pretty sure it's possible to write a boot manager that supports this feature. May be one of the third party ones already do?
      My System SpecsSystem Spec

  4. #4


    Orbiting the Moon
    Posts : 2,975
    Windows 10 x64


    Quote Originally Posted by Mexxi View Post
    Also, it supports XP which runs on FAT32 and Win8 supports upgrades from XP. I really doubt MS forces people to switch over to NTFS.
    Yes you are forced to NTFS since Vista: you cannot install the OS on fat32 because it has file size limitations and security flaws.

    If you upgrade to 8 from XP, if it's still fat32, (now who uses that combo anyway?) you will have to convert to NTFS or the upgrader will convert for you before copying files.

    So no fat32 for Win8. Ok, for usb sticks it's ok.
    Now I'm curious how you boot the VHD on a fat32 stick, because I've never tried that. I can tell you that the usb 2.0 To Go version is really slow. Maybe the VHD is faster...

    Maybe you're right about the unsupported boot on the multipart VHD, we'll see.
      My System SpecsSystem Spec

  5. #5


    Posts : 5
    Win8


    Quote Originally Posted by Hopachi View Post
    Yes you are forced to NTFS since Vista: you cannot install the OS on fat32 because it has file size limitations and security flaws.
    I know, still the boot manager is downwards compatible with XP and thus must support FAT32.

    Quote Originally Posted by Hopachi View Post
    If you upgrade to 8 from XP, if it's still fat32, (now who uses that combo anyway?) you will have to convert to NTFS or the upgrader will convert for you before copying files.
    True for the upgrades, but if you want to dual boot with an XP on a different (FAT32) HDD,then the boot manager has to support that too.


    Quote Originally Posted by Hopachi View Post
    Now I'm curious how you boot the VHD on a fat32 stick, because I've never tried that.
    That's exactly the problem at hand I have a functioning Win 8 vhd. I managed to install the boot manager properly on the FAT32 formatted stick. I split the vhd into 4GB chunks, but loading the first one makes the boot manager crap out. I assume that upon loading the vhd, the bootmanager checks its integrity and detects that the image isn't as big as its header may indicate, which in return would allow the conclusion that unlike virtualization software, the bootmanager is not capable of recognizing and loading multiple chunks.

    Quote Originally Posted by Hopachi View Post
    I can tell you that the usb 2.0 To Go version is really slow. Maybe the VHD is faster...
    I doubt that. According to an msdn blog I read vhd is supposed to perform 3% slower.The performance hit is probably barely notizable. While my stick supports USB 3.0,all the computers I tested it with only support 2.0. Performance is differing tremendously from machine to machine, depending on the chipset quality and performance. Still, working in Windows 8 To Go is butter smooth.

    I'm using a Sandisk Cruzer Extreme which according to benchmarks outperforms other high performance sticks in the 4K write by a whopping factor of 10. Deploying install.wim took less than 15 minutes. This is probably the reason why Windows 8 with its 130.000+ files still runs great off of it, despite USB 2.0. Still,I'm eager to see it boot up on a USB 3.0 capable comp


    Quote Originally Posted by Hopachi View Post
    Maybe you're right about the unsupported boot on the multipart VHD, we'll see.
    I plan on trying to boot a <4GB vhd off of the FAT32 stick tomorrow. Another idea would be to use parent and child vhds instead of splitting a single one into chunks.The former is apparently supported, so may be that'll work.
      My System SpecsSystem Spec

  6. #6


    Orbiting the Moon
    Posts : 2,975
    Windows 10 x64


    Right.

    Thanks for the post. We'll see tomorrow.
      My System SpecsSystem Spec

  7. #7


    Posts : 5
    Win8


    Alright, I tested my hypothesis. I used a slimmed down Windows 8 (2,3GB installed) on a fixed 4094MB vhd. Booting errored out with VHD_BOOT_INITIALIZATION_FAILURE on several machines. Converting the stick from FAT32 to NTFS without changing anything else actually made the whole setup work.

    Disappointing results in my eyes. In the meantime I also read Microsoft's white paper on vhd-performance where they also mention that running VHDs on FAT-drives is not supported. Their paper was based on Server 2008 R2 though. Trying to attach a VHD stored on a FAT-formatted partition in Windows 7 is denied. Apparently, Hyper-V doesn't allow it even though for fixed disks this hardly makes sense.

    Either way, due to explicit refusal of Hyper-V to load VHDs off of FAT-partitions, there's no point in trying to load split VHDs to make this work on FAT32. I'll mark this thread as solved. Even though it's not a solution to my problem, it's a definitive answer why my project won't work. I guess Win8 PE could be used with FAT32, but without VHD-encapsulation I'd rather choose the fully fledged portable OS.
      My System SpecsSystem Spec

Booting with multipart vhd possible?
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