When a site moves onto our hosting, one of the first things we switch off is its backup plugin. We do not need it, and on the server the site came from it was part of the load.
A VPS is one computer. That makes it easy to understand, and it also means the jobs that keep a site safe run on the same computer that serves the visitors. The backup is the clearest example.
What a Backup Costs a VPS
On a VPS, a backup is a job the server does to itself. A backup plugin or a script on a schedule works through the same steps:
- Read every file of the site.
- Dump the database, which lives on the same server.
- Compress both into an archive.
- Write the archive to the same disk.
- Upload it somewhere else, if that part is set up.
Every step uses the processor, memory and disk the visitors are using at the same moment. A plugin backup also runs inside WordPress, as PHP, so it takes a PHP process away from visitors and stops when WordPress is broken. Until the upload finishes, the newest copy sits on the disk it is meant to protect.
Why Night-Time Does Not Fix It
The usual advice is to run the backup at night. That assumes the server has a night. On our main web server the load is close to flat around the clock, so there is no quiet hour to hide a backup in. A site with visitors in other time zones, or a server shared by several sites, is in the same position.
How a Snapshot Works Instead
In public cloud the disk is not part of the computer. It is a separate storage volume attached to the server over the network, and the storage service can copy it without the server doing the work. That copy is a snapshot.
The web server spends no memory or processor time on it, no archive lands on its disk, and no plugin has to run. On our hosting the volumes that hold the sites are snapshotted every six hours. The database runs as its own service and is backed up continuously by that service, so the web server does not dump it either.
What a Whole-Server Snapshot Gets Wrong
If your VPS provider offers snapshots of the whole server, they take the backup load off the server. They do not separate the database, which on a VPS usually lives on the same disk as the site. A snapshot catches the database files in the middle of whatever they were writing, and restoring it is the same as recovering the database after a power cut. It usually works, and it is not something you want to rely on for a shop’s orders.
With the database on its own service, the disk snapshot only holds files, and the database has its own backups taken by the software that understands it.
The Same Rule for Disk Space
The backup is the easiest case to see, and a VPS bundles more than that. Its disk, memory and processors come as one size, chosen from a price list.
When the disk fills up, the site starts failing wherever it writes: sessions, uploads, logs. The error usually reads “No space left on device”, and it tends to show up as a form that returns a blank page rather than as an alert. The usual fix is the next plan up, which brings memory and processors nobody asked for.
In public cloud a storage volume can be made bigger while the server keeps running. The computer itself can also be swapped for a different size, with the same disks attached to the new one. We did that to one of our web servers this month: the disks and their snapshots stayed as they were.
When the Operating System Breaks
The operating system disk is a separate volume too. Ours are snapshotted every 48 hours, so an operating system update that goes wrong can be rolled back to the disk from before it, instead of reinstalling the server by hand.
The Copy for Distant Visitors
The CDN does the same for visitors. A page it has cached is served from a location near the visitor and does not reach the server at all, so the server only does the work that cannot be cached.
How We Run It
In our hosting the database, web server and CDN are separate services, the disks are separate volumes, and the backups are taken by the services that hold the data. That is why the backup plugin gets switched off when a site arrives.
Three Questions for Your VPS
- When your backup runs, which machine does the work? If it is the server that serves your site, every backup competes with your visitors.
- Where is the newest backup stored while it is being made? If the answer is the same disk, the most recent copy fails with the server.
- If the disk fills up, can it grow on its own, or do you need a bigger plan? If it needs a bigger plan, you will pay for memory and processors to get disk space.
If you run a VPS and want to know what its backups cost it, I am happy to look at how they are set up with you.
