Manual:$wgForeignFileRepos

Details
Properties required for all repos:
 * class
 * The class name for the repository. May come from the core or an extension. The core repository classes are LocalRepo, ForeignDBRepo, FSRepo.


 * name
 * A unique name for the repository.

For all core repos:
 * url
 * Base public URL


 * hashLevels
 * The number of directory levels for hash-based division of files


 * thumbScriptUrl
 * The URL for thumb.php (optional, not recommended)


 * transformVia404
 * Whether to skip media file transformation on parse and rely on a 404 handler instead.


 * initialCapital
 * Equivalent to $wgCapitalLinks, determines whether filenames implicitly start with a capital letter. The current implementation may give incorrect description page links when the local $wgCapitalLinks and initialCapital are mismatched.


 * pathDisclosureProtection
 * May be 'paranoid' to remove all parameters from error messages, 'none' to leave the paths in unchanged, or 'simple' to replace paths with placeholders. Default for LocalRepo is 'simple'.


 * descBaseUrl
 * URL of image description pages, e.g. http://en.wikipedia.org/wiki/Image:


 * scriptDirUrl
 * URL of the MediaWiki installation, equivalent to $wgScriptPath, e.g. http://en.wikipedia.org/w


 * articleUrl
 * Equivalent to $wgArticlePath, e.g. http://en.wikipedia.org/wiki/$1


 * fetchDescription
 * Fetch the text of the remote file description page. Equivalent to $wgFetchCommonsDescriptions.

ForeignDBRepo class:
 * dbType, dbServer, dbUser, dbPassword, dbName, dbFlags
 * equivalent to the corresponding member of $wgDBservers


 * tablePrefix
 * Table prefix, the foreign wiki's $wgDBprefix


 * hasSharedCache
 * True if the wiki's shared cache is accessible via the local $wgMemc

Defalut Value (code in Setup.php) :