SCCM OSD Troubleshooting: Fixing the Required Device Error

SCCM OSD Fails With “A Required Device Isn’t Connected or Cannot Be Accessed”

This is one of the more misleading errors you’ll see during a Configuration Manager task sequence — it sounds like a missing driver or a hardware fault, but it’s very often actually a WinPE networking/TFTP problem rather than anything to do with the target machine’s disk or drivers. A frequent cause is the RamDiskTFTPBlockSize setting on your PXE-enabled distribution point being set too high for your network path (some switches, VPNs, or WAN links don’t handle large TFTP block sizes reliably, which corrupts or stalls the boot image transfer and surfaces as this generic device error). To check and lower it:

1. In the Configuration Manager console, go to Administration > Distribution Points, right-click the relevant DP and open its Properties.
2. On the PXE tab, look for the RamDisk TFTP Block Size / Window Size settings.
3. Lower the block size (a smaller, more conservative value is generally more compatible across mixed network hardware) and retest the PXE boot.

If lowering the TFTP block size doesn’t resolve it, also double-check that the correct boot image architecture (x86 vs x64) is distributed to that DP and that any relevant mass-storage/NIC drivers are actually injected into the boot image the machine is using.

Screenshot: Distribution Point PXE / TFTP Settings

Other Common Causes of This Error

RamDiskTFTPBlockSize is a genuinely valid fix and remains the first thing to check, but it isn’t the only cause of this message. If lowering the block size doesn’t help, work through these in order:

• Missing or incorrect drivers in the boot image — the most frequent cause on newer laptops, particularly NVMe storage controllers and newer NIC chipsets that aren’t included in the default boot image.
• Boot image architecture mismatch — an x86-only boot image served to a UEFI x64 device (or vice versa) produces the same generic device error rather than a clearer message.
• DHCP scope options 66/67 misconfigured — especially in multi-subnet environments where IP helpers point PXE traffic at the wrong distribution point.
• WinPE running low on RAM — on memory-constrained devices, the ramdisk itself can fail to load reliably.