What is taking up all of our Microsoft 365 storage?

The number is pooled, which is why nobody owns it

SharePoint storage in Microsoft 365 is a tenant-wide pool: a base allocation plus an amount per licensed user, shared across every site. No single site has a quota that anybody feels, so no single site owner has a reason to care.

That’s the structural reason the number only goes up. It isn’t carelessness. It’s that the cost is collective and the effort of reducing it is individual.

The four things using it that you aren’t thinking about

Version history. SharePoint keeps up to 500 versions of a file by default. A 20MB presentation edited fifty times is a gigabyte, and every one of those versions counts against the pool. This is routinely the single largest line and almost never the one people guess.

Abandoned sites. A site created for a project that finished in 2022 still holds everything it held then. It also gets crawled, which means it’s still feeding search results and anything grounded on them.

The recycle bins. There are two, first-stage and second-stage, and content sits in them for 93 days. Deleting a large library doesn’t reduce your storage for three months.

Teams private channels. Each one creates its own site collection. An organisation with a hundred private channels has a hundred site collections, most of which nobody has ever looked at.

How to work out what you’re paying to keep

Three cuts, in this order. Each one is a different question and the answers rarely agree.

1. By site. Which sites hold the most. This tells you where to look and almost nothing about whether it should be there.
2. By library. Within the biggest sites, which libraries. This is where version history shows up as a number rather than a theory.
3. By file age. How much hasn’t been opened in two years, five years, ever. This is the cut that turns storage into a decision, because content nobody has opened since 2019 is either an archive candidate or a deletion candidate, and it isn’t a working file either way.

What to do with the three numbers

Set a version limit. Most organisations don’t need 500 and have never discussed it; a limit of 50 changes the growth curve immediately and affects nobody’s day.

Tier what must be kept. Content you’re obliged to retain doesn’t have to sit on the same storage as content people open daily, and the price difference is the point.

Delete what must not be kept. Retention obligations cut both ways: holding personal data past its purpose is its own exposure, not a safe default.

Then write the rule down, so this isn’t done by hand again next year. That last step is the difference between a cleanup and a lifecycle, and it’s what Storage & Archive Lifecycle delivers.

The free read

The Storage Analyser does the three cuts against your own tenant and returns them as one report. Ask for it on the page and we’ll send the package and the setup notes.

Five versions of the same document is also five answers for anything grounded on your content, which is the other reason this matters now.