Fast Startup in Windows 11: should you turn it off?

What Fast Startup actually does

Microsoft describes three startup modes: cold, wake from hibernation, and fast, which combines the two. When you shut down with Fast Startup on, Windows closes your apps and signs out every user, then saves the kernel memory image, including the loaded kernel-mode drivers, to hiberfil.sys and powers off. To you it looks like a full shutdown, even though the PC has gone through hibernation. Because you are signed out first, the file can be smaller: Microsoft lists a reduced hibernation file at 20% of physical memory by default, usable only by Fast Startup, against 40% for a full one.

Restart and Shut down are not the same

Microsoft states that the Fast Startup setting does not apply to Restart: a restart continues to perform a full boot cycle, because a restart usually means you want a completely new Windows state, for example after installing a driver. A plain Shut down is the opposite. Microsoft notes that the kernel, drivers and services are preserved and restored, not restarted, on user-initiated shutdowns, so the time between kernel reboots can be much longer than people expect. For one clean shutdown without changing any setting, run Shutdown /s /t 0: Microsoft documents a full shutdown as the default for Shutdown.exe.

When turning it off is worth it

Microsoft's position is that disabling it is not recommended, and it publishes no figure for how much boot time it saves on your PC. The reasons to turn it off are specific ones. A cold start takes longer than a fast one, so compare your own PC if the time matters to you.

• ✓Dual boot: Bazzite's dual-boot guide, for example, asks you to turn off Windows fast startup before you share a drive with it
• ✓You want every Shut down to reload the kernel and drivers, not only Restart
• ✓Keep it on if you only shut down and start up, and nothing is misbehaving
• ✓Wake on LAN is not a reason: see below

What it will not fix: Wake on LAN

Turning Fast Startup off does not make Wake on LAN work from Shut down. Microsoft documents Wake on LAN as supported from sleep (S3) or from hibernation you explicitly request, and not from Fast Startup or from a full shutdown (S5). Network adapters are deliberately not armed for wake in those states. The firmware on some PCs can still arm the adapter without Windows being involved, so check your BIOS or UEFI if you depend on it.

If shutting down returns you to the Lock screen

Microsoft documents one specific failure for Windows 10 and 8.1: with Fast Startup on, the shutdown fails and goes back to the Lock screen, and event ID 45 is logged in the System log, because a driver in the crash dump configuration did not load. Its resolution is to correct the DumpFilters registry value under HKEY_LOCAL_MACHINE\System\CurrentControlSet\Control\CrashControl so that dumpfve.sys is the only entry. Check for that event first; turning Fast Startup off hides the symptom without repairing the value.