Need to migrate the susite to a new main site

Question

In my microsoft tenant of the pooled storage of 25 TB 23.9 Tb were occupied and i need to migrate the subsite which contains 15 TB of storage into a new site in the same tenant whether it is possible.

Note that i have to perform this in one shot so i need an add-on for getting the additional storage of 15 TB

Answer 1

Dear @MOD Administrator,

I understand that you are concerned about moving a large volume of data from a subsite to a new site in order to free up storage space, as the current site is approaching the 25 TB storage limit.

According to Microsoft documentation: SharePoint limits - Service Descriptions | Microsoft Learn

Moving or copying content across sites is limited to a maximum of 100 GB per operation and no more than 30,000 files at a time. Given that your total data size is approximately 15 TB, the data will need to be divided into smaller batches and moved incrementally to the new site.

For more information on moving or copying files across SharePoint sites, please refer to the following article: Move or copy files in SharePoint - Microsoft Support

Please feel free to let me know if you have any further concern.

Answer 2

Migrating a 15 TB subsite into a new site in the same tenant in “one shot” is not supported because of SharePoint site size limits and how storage is managed.

Key points from the documented limits and behavior:

1. Per‑site size limit is 5 TB / 1 million items
   • For cross‑tenant and geo moves, a SharePoint site larger than 5 TB or with more than 1 million items cannot be moved; such moves fail.
   • While this example is for cross‑tenant and geo moves, it shows that a single SharePoint site is not supported at 15 TB of content for move operations.
2. Tenant storage is pooled, not pre‑allocated per site
   • By default, SharePoint Online uses a central storage pool from which all sites draw automatically.
   • Storage is not carved out per site unless manual limits are set; switching to pooled storage resets site limits to 25 TB, but the overall tenant storage cap still applies.
3. Current tenant storage is effectively full
   • With 23.9 TB used out of 25 TB pooled storage, there is not enough free capacity to duplicate or move 15 TB of content into a new site in one operation.
   • Even if there were enough tenant capacity, a single target site cannot exceed 5 TB for supported move scenarios.
4. Additional storage is purchased at the tenant level, not per site
   • Extra SharePoint storage is added as tenant‑wide capacity via add‑ons (for example, in 1 TB blocks).
   • This increases the total pool (for example, from 25 TB to 40 TB), but does not remove the 5 TB per‑site move limit.
5. Recommended approach (high level)
   Based on the documented limits, a 15 TB “one shot” move into a single new site is not feasible. A compliant approach must:
   • Break the content into multiple sites, each ≤ 5 TB and ≤ 1 million items.
   • Ensure the tenant has enough overall storage by purchasing SharePoint storage add‑ons before starting.
   • Plan migrations in batches rather than a single operation, respecting quotas and limits.

There is no supported add‑on that allows bypassing the per‑site 5 TB limit or performing a single 15 TB move into one site. Additional storage add‑ons only increase the tenant’s total capacity, not the supported size of an individual site or move.

---

References:

• Cross-tenant SharePoint migration
• Cross-Tenant Migration
• Manage site storage limits in SharePoint in Microsoft 365
• Add more SharePoint storage to your subscription
• Microsoft Sharepoint and storage addons for education
• Data Residency for SharePoint and OneDrive