Deciding on a Data Transfer Method
When performing the upgrade from Nexus Repository 2 to 3, there are three data transfer methods from which you must choose: HTTP downloading, file system copying, or file system hard linking. Each method has its pros, cons, and requirements as detailed below.
File System Hard Linking (Preferred)
Nexus Repository 2 tells Nexus Repository 3 the path of the file content to transfer. Nexus Repository 3 creates a file system hard link to the same content. With this method, data is not duplicated only new metadata files are created for assets in the new blob stores.
Pros: The fastest method, saves storage space
Cons: Both instances must be installed on the same server
Requirements
Both instances must be configured to access the same storage system on identically named mount points.
The file system must support hard linking.
There must be adequate file handles for both instances.
File System Copying
Nexus Repository 2 provides Nexus Repository 3 with the necessary path to file content, which Nexus Repository 3 then copies.
Pros: Faster than downloading, less impact on the performance
Cons: Not as fast as hard-linking
Requirements
Both instances must be configured to access the same storage system on identically named mount points.
Upwards of double the original storage space is needed during the upgrade.
HTTP Downloading
Nexus Repository 3 makes HTTP requests to Nexus Repository 2 to transfer configuration and data.
Pros: The only method that works for situations where Nexus Repository 2 and 3 are on different machines and do not share access to the same file system storage
Cons: This is the slowest option
Requirements
You must ensure you have enough storage space; upwards of double the original storage space will be needed at least temporarily during data duplication.