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A sandbox salesforce is simply a copy of your database you can use to test new ideas. As part of your Power of Enterprise Edition of Salesforce, you get for free six Developer sandboxes and one Developer Pro sandbox. The only difference between the two is that the Pro sandbox holds more data.

There are more differences.

A Full Sandbox can only be refreshed every 29 days, whereas a Partial Copy Sandbox can be refreshed every 5 days.

Only sample data is copied to a Partial Copy Sandbox on creation/refresh, whereas all data is copied over to a Full Sandbox.

For a Partial Copy Sandbox, The 5GB limit on file storage is different in addition to the overall data storage limit.

See this chart from Sandbox Licenses and Storage by Type.

Apparently, a Sandbox Template is also required for any Partial Copy Sandbox.

Sandbox Management Best Practices also has some recommendations for when to use each type of sandbox:

See also: Salesforce Developer Limits Quick Reference.

Sandbox Limits

You can refresh a Full sandbox 29 days after you created or last refreshed it. If you delete a Full sandbox within those 29 days, you need to wait until after the 29 day period, from the date of last refresh or creation, to replace it.

You can refresh a Partial Copy sandbox 5 days after you created or last refreshed it. If you delete a Partial Copy sandbox within those 5 days, you need to wait until after the 5 day period, from the date of last refresh or creation, to replace it.

You can refresh a Developer or Developer Pro sandbox once per day. Enterprise Edition includes licenses for 25 Developer sandboxes and 1 Partial Copy sandbox.

Performance Edition includes licenses for 1 Full sandbox, 5 Developer Pro sandboxes, 100 Developer sandboxes, and 1 Partial Copy sandbox.

Unlimited Edition includes licenses for 1 Full sandbox, 5 Developer Pro sandboxes, and 100 Developer sandboxes and 1 Partial Copy sandbox.

Professional Edition includes licenses for 10 Developer sandboxes. (Change sets aren’t available.)

If you need licenses for more sandboxes, contact Salesforce to order sandboxes for your organization.

Sandbox Storage Limits

Partial Copy sandboxes have a 5 GB of files and a 5 GB of data storage limit.

Developer Pro sandboxes have a 1 GB of files and a 1 GB of data storage limit.

Developer sandboxes have a 200 MB of files and a 200 MB of data storage limit.

Full sandboxes have the same storage limit as your production organization.

Sandboxes don’t send email notifications when storage limits are reached. However, if you reach the storage limit of your sandbox, you can’t save new data in your sandbox. To check your storage limits, from Setup, enter Storage Usage in the Quick Find box, then select Storage Usage in your sandbox.