Add first File Server structure draft

Architecture.md

@@ -8,5 +8,43 @@
 
 **Worker's** main role is securely _compile_, _run_ and _evaluate_ given submit against model solutions provided by author of each task. It is logicaly divided into three objects:
 - **Message Frontend** communicates with **WebApp** using messaging queue [ZeroMQ](http://zeromq.org/). It receives new submits, operates the evaluation through **Work API** and reports progress back.
-- **Worker Core** can do all evaluating steps and is responsible for security of them. Great sandbox [Isolate](https://github.com/ioi/isolate) is used.
+- **Worker Core** can do all evaluating steps and is responsible for security of them. Sandbox [Isolate](https://github.com/ioi/isolate) is used.
 - **File Server Frontend** ensures via **File API** access to files on **File Server**, where are stored testing inputs and corresponding outputs for each task and other required files. It's possible to upload files, too.
+
+## File Server
+![File Server Infrastructure](https://github.com/ReCodEx/GlobalWiki/blob/master/images/File_Server.png)
+
+**File Server** stores data, which is better keep out of **WebApp's** database. It should meet following requirements:
+- store files without duplicates
+- keep consistent state with main database
+- serve files to workers on demand
+
+To meet these requirements, **Storage** and **Database** must be set as bellow.
+
+### Storage
+**Storage** is meant as disc space with some commonly used filesystem. We'll use `ext4`, but the other ones should work too. **Storage** file structure is:
+```
+.
+├── submits
+│   └── user_id
+│       └── advanced_dot_net_1
+│           ├── bf216fa9274261628f4d952a103c6cfd1cbbc587
+│           └── e6ae49bbfda4a8bb57aceeb64fb117990b226ca5
+├── tasks
+│   ├── a
+│   │   ├── a014ed2abb56371bfaf2b4298a85d5dfb56509ed
+│   │   └── a5edbd8b12e670ed1e3110d6c0524000cd4c3c7a
+│   └── b
+│       └── b1696358b8540923eb79b68f95c0f94c13a83fa7
+└── temp
+    └── 1795184136b8bdddabe50453cc2cc2d46f0f7c5e
+```
+- **submits** keep information about all files submited by users to ReCodEx. There are subdirectoris _user_id_ and _advanced_dot_net_1_ which divides submits by users and class they took part of. This structure is easy to maintain for new and deleted users.
+- **tasks** contains all files for all existing task in ReCodEx. To avoid too much files in one directory, files are separated to subfolders by first character of their name.
+- **temp** directory is dedicated to temporary storing outputs of programs on teachers' demand. This directory will be erased by cron job on daily basis.
+
+### Database
+For user friendly access and modifying tasks following information should be stored in database:
+- list of tasks with their newest version number
+- for every task and version list of used files (their hashed names)
+- for every hash name one human readable filename