core_file_storage table in Magento with very huge size. What is it's functionality? Can I remove and replace functionality? Is it affects to the speed of my database? Thanks.
Magento can store media files in database.
Configuration \ Advanced \ System \ Storage Configuration for Media.
The main reason for storing media in database is the case when you use balancing servers and don't want to bother with shared directories. All the rest is performance degradation.
I suggest switching to filesystem storage. Files will be synchronised automatically by Magento with click on "Sync" button at the admin screen posted above.
This table is backed by: Mage_Core_Model_File_Storage
It stores media files, as BLOBs in the DB, and can lead to issues with performance.
The intent behind this is for distributing the Media files across a larger installation, or even being able to extrapolate the storage system into something besides mysql or files.
The settings for this are in the admin: Configuration->Advanced->System->Storage Configuration for Media. Switching that setting to files, should remove the files from that table, thus shrinking it.