MogileFS由Danga Interactive 公司开发出来的分布式文件系统，为解决当时所运营的LiveJournal站点的存储难题而产生。
|thing that wants to store/load files
|the database that stores the MogileFS metadata (the namespace, and which files are where). This should be setup in a HA config so you don’t have a single point of failure.
|event-based parent process/message bus that manages all client communication from applications (requesting operations to be performed), including load balancing those requests onto “query workers”, and handles all communication between mogilefsd child processes.
|where files are stored. The storage nodes are just HTTP servers that do DELETE, PUT, etc. Any WebDAV server is fine, but mogstored is recommended. mogilefsd can be configured to use two servers on different ports… mogstored for all DAV operations (and sideband monitoring), and your fast/light HTTP server of choice for GET operations. Typically people have one fat SATA disk per mountpoint, each mounted at /var/mogdata/devNN.
|A domain is the top level separation of files. File keys are unique within domains. A domain consists of a set of classes that define the files within the domain. Examples of domains: fotobilder, livejournal.
|Every file is part of exactly one class. A class is part of exactly one domain. A class, in effect, specifies the minimum replica count of a file. Examples of classes: userpicture, userbackup, phonepost. Classes may have extra replication policies defined.
|minimum replica count (mindevcount)
|This is a property of a class. This defines how many times the files in that class need to be replicated onto different devices in order to ensure redundancy among the data and prevent loss.
|A key is a unique textual string that identifies a file. Keys are unique within domains. Examples of keys: userpicture:34:39, phonepost:93:3834, userbackup:15. Fake structures work too: /pics/hello.png, any string.
|A file is a defined collection of bits uploaded to MogileFS to store. Files are replicated according to their minimum replica count. Each file has a key, is a part of one class, and is located in one domain. Files are the things that MogileFS stores for you.
|A fid is an internal numerical representation of a file. Every file is assigned a unique fid. If a file is overwritten, it is given a new fid.