How SharePoint Online Stores Files in the Preservation Hold Library

Preservation Hold Library Now Holds Files With Version History

During a recent content search for some documents, I noticed that the search found far fewer versions of SharePoint Online files than was the case in the past. This is the effect of the change introduced in mid-2022 (or rather, delayed until August 2022) documented in message center notification MC288633 (Microsoft 365 roadmap item 82062). I discussed the potential for the change when Microsoft first announced their intention to implement it in October 2021. Now it’s time to see how things work in practice.

In a nutshell, from the time Microsoft deployed the change to a tenant, SharePoint Online stops storing multiple copies of retained files in the Preservation Hold Library. Instead, SharePoint follows the same approach as taken for regular files stored in document libraries and stores a single file containing its full version history. Files end up in the Preservation Hold Library when SharePoint must retain them because of a retention policy applied to the site, a retention label applied to individual files, or eDiscovery holds. In all cases, files remain in the Preservation Hold Library until the hold applied by retention or eDiscovery lapses.

Site owners don’t have to create the Preservation Hold Library as SharePoint creates it automatically when required. To view Site items in the Preservation Hold Library, add /PreservationHoldLibrary to the site URL in the browser bar.

Difference in File Storage

Figure 1 shows how SharePoint used to store Office documents in the Preservation Hold Library. Each version is stored as a separate file with no versions. If the user updates the file, SharePoint creates a new version in the Preservation Hold Library to capture the changes and make them available for eDiscovery.

The example in Figure 1 comes from January 2022, before Microsoft deployed the change. Examining a more recent entry in the Preservation Hold Library, we see that different versions of the file are available (Figure 2).

It’s easy for changes like this to pass by without being noted, especially when Microsoft delays the deployment of an update for one reason or another (in this case, it was to give customers more time to prepare).

A practical effect of the change is that eDiscovery searches find the latest version of retained files. If investigators want to see previous versions, they can view or restore that version.

Storage Quotas

One of the issues with the way that SharePoint Online captures files for retention is the large amount of storage consumed for this purpose. Given that SharePoint storage is expensive, this is bad news.

In Figure 3, we see that SharePoint uses 20.6 GB or 21.87% of the overall site storage. Even though I know that this site holds many copies of large chapter and book files for the Office 365 for IT Pros eBook, 20.6 GB of retained content is quite a chunk.

The good news is that the advent of multi-version storage seems to have reduced the storage used by retention by a couple of percentage points over what it was in 2021. It’s probably too early to be definite on this point, but the signs are good. My expectations are that the overall storage used by the preservation hold library should reduce over time as older files reach the end of their retention period and SharePoint removes them from the library. We’ll see.

It’s taken me too long to comment on the Preservation Hold Library change. Sometimes life gets so busy that good changes go by ignored. This is a good change.

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