Duplicate Attachments will duplicate the attachment and thumbnails, instead of letting WordPress regenerate them. This saves an enormous amount of time and will also preserve any manual changes to the thumbnails.
For example, a post with 5MB of attachments, broadcasted to two blogs:
With normal attachment copying: 30 seconds
With Duplicate Attachments: ~1 second
Activate the plugin in the pack and then check that your existing attachments action is to delete and replace. The plugin will take over copying of attachments automatically from then on.
Comparison of attachment-related plugins
|Feature||Basic||Duplicate Attachments||Protect Child Properties||Update Attachments|
|Keeps existing attachments1||Choice||No||Choice||✓|
|Thumbnail regeneration speed2||Slow||Fast||Slow||Slow|
|Updates existing files in place||No||No||No||✓|
1 If several posts share the same attachment and it is deleted before broadcasting, the attachment ID will not match that of the newly-copied attachment. Otherwise the automatic deletion of attachments before broadcast is not a problem.
2 Regeneration occurs when an image attachment is copied to the child blog for the first time.
Admin > Broadcast > Misc tab > Existing attachments