####Defination: SeaweedFS is a simple and highly scalable distributed file system, two objectives as follows:
- to store billions of files!
- to serve the files fast!
####Fetures:
- implement only a key->file mapping ,like "NoSQL" ,called "NoFS"
- there are master-server and volume-server:
######master-server:
- the central master only manages file volumes
######volume-server:
- volume servers manage files and their metadata
######master server - volume server
- The actual data is stored in volumes on storage nodes
- One volume server can have multiple volumes
- All volumes are managed by a master server
- master server contains volume id to volume server mapping
- 每个 VolumeServer 都维护个 n 个 Volume ， 每个 Volume 都有一个专属 VolumeId， Needle 属于 Volume 里面的一个单元
######purposes for these designs:
- relieves concurrency pressure from the central master
- spreads file metadata into volume servers, allowing faster file access (just one disk read operation).
######seaweedfs - structers
- 拓扑结构：【DataCenter, Rack, DataNode】
- 存储模块：【Store, Volume, Needle】
- 在 MasterServer 维护的拓扑结构里， 是把 VolumeServer 的相关信息存储在 DataNode 里
######fid
fid: 3,01637037d6
a volume id: 3
one file key: 01
a file cookie: 637037d6.
- volume id : an unsigned 32-bit integer
- file key : an unsigned 64-bit integer
- file cookie : an unsigned 32-bit integer - to prevent URL guessing
######replication parameter options:
- SeaweedFS applies the replication strategy at a volume level
- 000: no replication
- 001: replicate once on the same rack
- 010: replicate once on a different rack, but same data center
- 100: replicate once on a different data center
- 200: replicate twice on two different data center
- 110: replicate once on a different rack, and once on a different data center
#######Storage Size
- each volume can be 8x2^32 bytes (32GiB)
- There can be 2^32 volumes
- total system size is 8 x 2^32 bytes x 2^32 = 8 x 4GiB x 4Gi = 128EiB
- Each individual file size is limited to the volume size
######TTL 定时删除
####参考链接