Pulling the power causes everything to stop in flight, with no warning. kill -9 has the same effect on a single process, forcefully terminating it with a SIGKILL.
If a process is killed by kernel or power outage, it doesn't do any clean-up. That means you could have half-written files, inconsistent states, or lost caches. You usually don't have to worry about any of this because of journaling, exit status and battery backup.
Temporary files in /tmp will be automatically gone if they are in tmpfs, but you may still have application-specific lock files laying around to remove, like the lock and .parentlock for firefox.
Most software is smart enough to retry a transaction if it doesn't record a successful exit status. A good example of this is a typical mail system. If a message is being delivered, but gets cut off in the middle, the sender will retry later until it gets a success.
Your filesystem is probably journaled. If you are moving or writing a file and it dies mid-stream, the journaled file system will still reference the original. The journaled filesystem will make changes non-destructively, leaving the old copy, then only reference the new copy as a last step before reclaiming space the old copies occupied on disk.
Now if you have a RAID array, it has all kinds of memory buffers to increase performance and provide reliability in a power failure. Most likely your filesystem will not know about the caches in the device and their state, so it thinks a change has been committed to disk, but it is still in the RAID cache somewhere. So what happens when the power dies? Hopefully you have a functional battery in your RAID enclosure and you monitor it. Otherwise you have a corrupt file system to fsck.
Yes, a few bits can become corrupted in a binary, but I would not worry about that much on modern hardware. If you are really paranoid, you can monitor the health of your disks and RAID with the appropriate tools, but you should be doing that anyway. Do regular backups and get an Uninterruptible Power Supply.
On the Dell R710 (and many other makes/models) you can monitor the power usage yourself with this command:
# ipmitool sdr list | grep Watts
System Level | 84 Watts | ok
That's the linux version, but there are Windows equivalents. Graphing that in your favorite tool is left as an exercise for the reader. It should be noted that this gives the power draw into the motherboard. Power supplies are not ever 100% efficient, so add about 15% to that number to get the input into the power supply. Or connect it to a watt meter and measure the efficiency yourself. PSUs are most efficient in the middle of their stated range, somewhere about 50-60% of the rated capacity.
If you are concerned about power usage you might consider using an L-series processor.
What happens when you draw more? That depends on the provider. You'll likely just get a warning (if they even notice at all.) And that's also the scary part. What if everyone draws just over and the circuit breaker trips? How closely do they monitor those circuits? Is it active monitoring or passive monitoring (is there a meter on the circuit or do the building engineers do spot checks with a clamp on meter?) If there is a meter is it per power port or per circuit?
Overall, it's just best to monitor the draw yourself.
How do you know before you order the server? Well, that's a guessing game. Unless you're really cranking on the HW you won't get near the peak.
Best Answer
You can try a clamp-on meter, but the HP Management Software works as well :)
You can download the appropriate HP software for your server model/generation/OS from here.
Are you on Windows or Linux? What generation is your DL360? If you don't want to dig into the GUI of the HP Management Agents on Linux, the
hpasmcliutility will show the power supply reading on demand in Watts. Depending on the version of the utility/server, you may see individual power supply readings or the system's power meter reading:or