We Moved the File Server While It Was Running. Nobody Had to Log Off.

Most offices think of a server move the way they think of moving house. Everything goes in boxes, nothing works for a while, and somebody has to pick a day when it hurts the least. For a long time that picture was accurate. It does not have to be anymore.

Last week one of our clients needed two of its servers moved. One was the file server, the place where every department keeps its shared folders, with a little more than eight hundred gigabytes on it. The other was a small server that runs a building system. Both lived on an older host machine, the physical box that runs several servers at once. We had planned to upgrade that host in place. It could not be done cleanly, and the honest fix was a fresh install, which means the servers on it had to go somewhere else first.

So we moved them while they were running. The small server took about ten minutes. The file server took about two hours. Neither one was shut down, and nobody was asked to save their work and log off. On Monday the staff opened their shared folders the way they do every morning, and nobody noticed a thing, which is exactly the point.

What actually moves

Most office servers today are not physical machines. They are virtual machines, a complete server that lives as a set of files on a bigger host. Because it is software, it can be copied from one host to another while it keeps working.

The copy happens in passes. The first pass sends the whole memory and disk across the network while the server keeps serving files. Anything that changes during that pass gets sent again, and again, each round smaller than the last. When what is left is tiny, the server pauses for a moment far too short for anyone to notice, the last few changes go across, and it carries on running on the new host. A person in the middle of saving a spreadsheet sees nothing.

What has to be in place first

It is not magic, and it is not free of preparation. A few things have to be true before you try it.

Both hosts have to trust each other. They need to be part of the same network and the same sign-in system, with permission set up for one to hand a running server to the other. That is an afternoon of careful setup the first time, not a checkbox.

The new host needs room. Enough memory for the server you are moving and the ones already there, and enough disk for every gigabyte of it. We checked both before we started, because a move that runs out of space halfway is worse than no move.

The network between them has to be fast and dedicated. Two hours for eight hundred gigabytes is a good result, and it comes from keeping that traffic off the network your staff use.

And you need a backup you trust before you touch anything. We would not move a file server we could not restore.

Why the old host is staying

The tempting thing to do with an old host is to throw it out. We are doing the opposite. It gets a fresh, clean install and stays in the rack as a spare.

The reason is the same trick in reverse. If the newer host ever needs maintenance, or has a fault, the servers can move back onto the spare the same way they moved off it, while they run. A machine that would have been scrap becomes the reason a hardware problem does not turn into a day off for the whole office. And because that fresh install does not touch anything anyone is using, it does not need a closed day either.

What to ask your IT people

If your servers live on a single host, ask what happens the day that host needs to be rebooted, repaired or replaced. If the answer involves a closed day, ask whether it has to. Sometimes it does. Often it does not, and the difference is a second host and an afternoon of setup.

If your servers all live on one host, what happens the day that host has to be rebooted, repaired or replaced, and does it really have to cost you a day?