DHCP pair messed up, second one only running cant get primary up.

Bob Harold rharolde at umich.edu
Mon Jan 16 19:48:41 UTC 2017

On Mon, Jan 16, 2017 at 12:14 PM, Drew Derbyshire <swhobbit at derbyshire.us>

> As an aside ...
> The thought of putting recovery state/log files (i.e. the DHCP leases file
> and its backup) on a RAM disk to make top look pretty leaves me dismayed.
> That leaves zero local protection against a system crash (or misguided
> deliberate reboot).
> And yes, the server has been running 346 days -- Doesn't matter. Services
> can be five nines reliable, but hardware won't be.
> An SSD, or if you prefer multiple SSD units configured as a raid, will
> give you the same order of performance without the premortem fodder.
> The machine should be audited for other critical files which are written
> to volatile storage, and moved to the SSD or other storage as well.
> -ahd-
I agree that putting state in ram is a concern, but with a failover pair,
there should be a duplicate copy on the other server of all but the very
latest changes.  There is a risk when one server is rebooting, so having a
copy of the backup lease file on real disk would help.
I think SSD (particularly write speed) is still orders of magnitude slower
than ram.

That said, I would not ever want to have both servers rebooted at the same
time, or even restart DHCP at the same time.  Restart one, allow it to sync
data and get to normal-normal, then restart the other.

Bob Harold
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