ESXi 5 Won’t Boot From USB

I’ve been upgrading my home VMware lab to vSphere 5.1 today and ran into an issue that I thought I would share.  I had previously written about my home lab environment – I run HP xw8600 workstations, and because I’m using SATA disks behind a SAS controller they are being seen as ‘remote’ disks to the ESXi installer.  This means that I need another type of disk that will be seen as a ‘local’ disk so ESXi can create a scratch partition.  A USB thumb drive was the answer, but not without issues.

When I installed ESXi 5.0 on the thumb drive, the install completed without problem, but after the post-install reboot ESXi 5 failed to boot.  I received a non-system disk / no bootable device error.

When I installed ESXi 5.1 on the same thumb drive, the install completed without problem, and again, after the post-install reboot ESXi failed to load.  On ESXi 5.1, however, I didn’t receive an error, but just had a blinking cursor in the upper left corner of an otherwise blank screen.  The cursor just blinked endlessly – no ESXi loaded.

The fix was the same for both 5.0 and 5.1, even though the symptoms were different.  Because I’m running on vintage hardware, my BIOS does not support booting from GUID Partition Table (GPT) partitions.  As of vSphere 5.0, VMware changed the partitioning layout of the system disk from Master Boot Record (MBR) to GPT.  My motherboard does not have a UEFI option, so booting from GPT isn’t going to work.  A GPT is not necessary on a 4GB thumb drive (GPT is necessary for partitions over 2.20TB), so the fix was to simply format my system disk as MBR.  There is an install option in the ESXi installation routine to force the system disk to be formatted with MBR instead of GPT, enabling ESXi to boot correctly.  Here’s how to enable ESXi to format the installation disk with MBR:

1.) Boot server from ESXi installation media.

2.) Wait for prompt in lower left-hand corner that says <SHIFT+O: Edit boot options> .  Press SHIFT+O (that’s the letter O, not a zero).

SHIFT+O Edit Boot Options VMware ESXi

3.) In the lower-left hand corner, after the word ‘runweasel’ insert a space then type formatwithmbr.  Press enter to continue the installation process.

runweasel formatwithmbr

ESXi should now install as normal.  After the install, you should find that your server (workstation) boots into ESXi.  If it doesn’t, you may have to play with BIOS options a bit more.  I’ve heard of AHCI mode causing issues with boot from USB, as well as incorrect boot order, and simply enabling the boot from USB option in BIOS.  Aso, check to see if your server/workstation can support an EFI image instead of traditional BIOS.

If you are interested in some other ESXi boot options, see here:

When using the formatwithmbr option, the VMFS paritition created on the boot disk will be formatted as MBR.  Any other VMFS partitions that are created on other disks in your system will be formatted with GPT per the vSphere Storage section in the official vSphere 5 documentation set.


  1. I have ancountered exactly the same problem with ESXI 5.1 and HP ProLiant DL360 g7. The solution worked for me too.
    What is bothering me is the fact that the same ESXI 5.1 wokred perfectly (on default settings) on a regular PC and not on super-hyper ProLiant.

  2. Perfect. Is this documented somewhere? You saved me an unknown but easily foreseeable hours of time!

  3. Thank you so much, this worked a treat and I am sure saved me hours 😉

  4. Thank you, this saved me a lot of time.

  5. Christian says:

    Thanks a lot Josh!
    Great job, works perfectly.

  6. Thank you very much!!!!! I’ve worked for hours by using vSpere and your last one sentence saved me in 1 mins…
    “Aso, check to see if your server/workstation can support an EFI image instead of traditional BIOS.”

  7. Thank you. I already spent two days trying to find a solution to this problem. I am glad I found your site.

  8. Worked perfectly for me too. Thanks a lot for the time saved !

  9. Same, i was having issues with this on a machine that after a few reboots kept corrupting the main GPT, forcing a restore… so i figure using MBR will solve this issue… at least i hope it does!

  10. Fantastic. Has problem with my HP Microserver G8 and this helps!! Thanks!!

  11. Thanks alot good sir. Saved me a major headache and alot of lost hours!

  12. Michael says:

    Thanks. This was a perfectly titled, accurate, no BS, quick understandable guide. Used 30 minutes on HP’s crapforums until another way of googling lead me to this. Thanks!

  13. Thank YOU. I have been struggling with boot from USB and SSD disks !! i wish i have found your simple and easy guide month ago.. Thank you this site is a keeper

  14. SUPER!!!!

  15. Thnxs you are the Best !!!
    I instaled esxi 5.1 on : Hp Dl320g4, Hp ML 110 G5, Hp ML150 G3, Hp ML110 G6, Hp ML110 G7… IBM x3200 M1 & M2, IBM x3250 M1 & M2… and now I tried to install on Hp DL120 G7… and not boot after instalation. Never have to make nothing… I install on SanDisk Cruzer Fit 4Gb USB Thumb (very litlle and have Light Read/ the Hp ISO or IBM ISO.
    I dont understand why…. a Hp Dl120 G7 dont boot… but your save me !!! your site its the best. Thanx a lot and sorry for my bad english from Buenos Aires – Argentina.

  16. Thankyou!

  17. Thank you so much!!!!

  18. hydrozyk says:

    Wow! This fixed it for me. Thank you thank thank you!


  1. […] writing this post, I found out about ESXi 5 Won’t Boot From USB which solves this exact problem for an HP XW8600 configuration (those are slightly larger machines […]

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