I would like to stop carrierwave deleting a file

Well AFAIK remove_previously_stored_files_after_update only work when a model object is updated so setting it to false will not remove the old file during update

But in your case you have to ensure the file are still present when the related model object is destroy

well I dont think there(if you examine the code here) is any mechanism currently available in in Carrierwave do that

but you can overwritten the remove! to achieve the same I guess this involve setting up attr_accessor (which is flag to decide whether to keep the file or delete it)

Inside your desired Model define a attr_accessor (say keep_file)

and in the desired uploader override the remove! method

class MyUploader < CarrierWave::Uploader::Base 
  def remove!
     unless model.keep_file
       super
     end
  end
end

and ensure that you set the attr_accessor for the object (if you want to keep the deleted file) before destroying them

Example

u = User.find(10)
u.keep_file = true
u.destroy 

This will ensure that file are cleaned up when the record is deleted from database

Let me know if there any better to do this

Hope this help

Actually there is a way to do this, you just need to skip callback that deletes it:

skip_callback :commit, :after, :remove_<column_name>!

for example

# user.rb
mount_uploader :avatar
skip_callback :commit, :after, :remove_avatar!

see https://github.com/carrierwaveuploader/carrierwave#skipping-activerecord-callbacks

Keeping files for all, or some uploaders

CarrierWave.configure do |config|
  config.remove_previously_stored_files_after_update = false
end

If you want to configure that on a per-uploaded basis:

class AvatarUploader < CarrierWave::Uploader::Base
  configure do |config|
    config.remove_previously_stored_files_after_update = false
  end

  ...
end