I'm unsure where I could be going wrong at this point - maybe someone has an idea that I haven't thought of yet?
This is a new install, so there is no config file or existing data to be preserved.

Here's the machine I'm attempting to boot unRaid on:
- Dell T7810
- 2X Intel Xeon E5-2690 v4
- 128GB DDR4 Memory
https://www.amazon.com/gp/product/B095TRGCSX/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1

 

I have purchased this SAS HBA to connect my drives to this server, as the chassis only has space for 2 3.5" drives inside.
https://www.amazon.com/dp/B0BKQDJLZ9?ref=ppx_yo2ov_dt_b_fed_asin_title&th=1

I've since flashed this HBA into IT mode, and it seems to be working fine - upon booting, the server lists both the HBA and all four connected drives as expected.

 

I've used this machine as a bare-metal Ubuntu server in the recent past, so I doubt there are any major hardware issues.
I have tried using both the USB creation tool and the manual method, with unRaid versions 6.12.13 and 6.12.11. All of these have behaved the same.

When I try to boot using UEFI mode, I simply get a blank screen for ~5 minutes before the server reboots. Nothing appears on the screen at any point after BIOS.
When I try to use Legacy mode, I am able to get into the syslinux selection - but when I try to boot 'Unraid OS', I get 3 "OK"s into the boot sequence before the server suddenly reboots.
GUI Mode and GUI Safe Mode both result in the same behaviour as above, while non-GUI Safe Mode gets through 'Loading /bzimage... ok' and 'Loading /bzroot... ok' before getting stuck and idling there until I forcibly power the server down.

In a reddit thread, someone suggested adding the intel_iommu=on and iommu=pt flags to the 'Unraid OS' boot option for specifically Dell servers.
Doing this results in the same behaviour as non-GUI Safe Mode (gets past /bzroot, then freezes).
Thread: https://www.reddit.com/r/unRAID/comments/uyxv83/unraid_wont_boot_after_os_upgrade/

Is there anything obvious I'm missing? I'm really hoping there is. Thanks for your help.

Some Dell servers are known to be problematic booting Unraid, did you try 7.0.0-beta? The different kernel may help.

There have also been reports that formatting the flash drive using Rufus during the Manual install method can sometimes help.

2 hours ago, itimpi said:

There have also been reports that formatting the flash drive using Rufus during the Manual install method can sometimes help.

Thank you for the suggestion! Unfortunately, formatting the drive with Rufus did not seem to have an effect. Attempted with version 6.2.13, with both UEFI and Legacy modes.

 

 

4 hours ago, JorgeB said:

Some Dell servers are known to be problematic booting Unraid, did you try 7.0.0-beta? The different kernel may help.

You're a lifesaver. I'll admit I don't love the idea of running beta software on this server, but it's better than no software!
UEFI mode is unchanged, but I am able to boot using Legacy mode on version 7.0.0-beta.3.
Thank you so much!

51 minutes ago, atkion said:

I'll admit I don't love the idea of running beta software on this server

Should be fine, I've been running it on both my productions servers for some time.

System Specs:

Dell T7810
Dual Xeon E5-2695 v3
128 GB ECC RDIMM RAM (2x64 GB)
I encountered freezing and rebooting issues when attempting to boot Unraid 7.0.0 RC2 on my system. Based on the errors during boot, I modified my syslinux.cfg file to include specific kernel parameters, which resolved the issue.

 

default menu.c32
menu title Lime Technology, Inc.
prompt 0
timeout 50

label Unraid OS
  menu default
  kernel /bzimage
  append initrd=/bzroot intremap=no_x2apic_optout mce=off clocksource=hpet

label Unraid OS GUI Mode
  kernel /bzimage
  append initrd=/bzroot,/bzroot-gui intremap=no_x2apic_optout mce=off clocksource=hpet

label Unraid OS Safe Mode (no plugins, no GUI)
  kernel /bzimage
  append initrd=/bzroot unraidsafemode intremap=no_x2apic_optout mce=off clocksource=hpet

label Unraid OS GUI Safe Mode (no plugins)
  kernel /bzimage
  append initrd=/bzroot,/bzroot-gui unraidsafemode intremap=no_x2apic_optout mce=off clocksource=hpet

label Memtest86+
  kernel /memtest

 

Why These Kernel Parameters?

1. intremap=no_x2apic_optout
Purpose: Disables x2APIC IRQ remapping to prevent issues with incomplete BIOS support.
Error Addressed:

DMAR-IR: Enabled IRQ remapping in x2apic mode
x2apic IRQ remapping doesn’t support interrupt remapping

2. mce=off
Purpose: Suppresses Machine Check Exceptions (MCE) temporarily to allow the system to boot.
Error Addressed:

mce: [Hardware Error]: CPU 0: Machine Check Exception: 5 Bank 0: f2000000000a0005
mce: [Hardware Error]: Processor context corrupt

3. clocksource=hpet
Purpose: Forces the use of HPET (High Precision Event Timer) as the system clocksource, which is more stable on problematic hardware.
Error Addressed:
TSC 8bc41149e62f TIME 1735736396 SOCKET 0 APIC 0 microcode de 49
Detailed Error Analysis:
Error: x2APIC IRQ Remapping
Cause: The system initializes Intel VT-d (IOMMU) and IRQ remapping, but incomplete BIOS support for x2APIC causes instability.
Solution: Disable x2APIC remapping via the intremap=no_x2apic_optout parameter.
Error: Machine Check Exception (MCE)
Cause: Low-level CPU errors due to microcode incompatibility, BIOS/kernel misconfiguration, or hardware instability.
Solution: Temporarily suppress MCE with mce=off to isolate the issue. Update BIOS and microcode as a long-term fix.
Error: Unstable TSC Clocksource
Cause: Timing issues common on multi-socket systems like the Dell T7810.
Solution: Force a stable clocksource with clocksource=hpet.

 

Final Notes:
If you're facing similar issues, try adding these parameters one at a time to narrow down the root cause. For me, adding all three resolved the problem.

If this helps you or you have further insights, feel free to share!