Why do servers in general boot so slow?

If there is 1-2 TByte RAM in them, it could take 10-20-30-40 minutes to cold boot a server..Why is that? Isn't memory extreme fast in average? Why do the "tests"(?) need so much time?

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    You want to be sure the hardware works, right? The stakes are a lot higher than with your personal computer. If you need the time back, that's what kexec (Linux) and soft restart (Windows Server 2016) are for. Dec 28, 2017 at 9:16

2 Answers 2


Servers use ECC memory. When powering up, the memory and the ECC bits are in a somewhat random state and reading a previously unwritten address would trigger a memory/ECC fault.

So, the memory has to be initialized to a determinate state, ie. written to - with several hundred GB or even TB this takes a while. On a warm reboot, this isn't necessary and should be skipped by the firmware.

Also, RAID controllers take quite a bit longer to initialize, partly due to the larger number of disks, possibly staggered spin-up, and integrity checks.


Any classic system would boot way slower if it were to perform detailed hardware tests.

To see an example, disable 'fast memory check' in a desktop's BIOS and you'll see how much an actual hardware test takes.

So to answer, this is like it is because for servers hardware integrity is the most important aspect.

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