1. What's PureFlash

PureFlash is a ServerSAN system designed for flash based storage device, such as PCIe flash card, NVMe SSD, SATA SSD. PureFlash has the following features:

1. provide block storage to client
1. multi-replications on different for data protection
1. multi-path for client
1. RDMA based client access
1. thin provision
1. uninterruptedly scale out
1. volume snap shot
1. volume clone

2. Why need a new ServerSAN software?

Flash storage device is totally different than traditional HDD. The essential different is that SSD don't need seek time before read/write. So SSD has outstanding random read/write performance.

Almost all traditional storage system has a deep software stack from client's access to data's stored on disk. This deep software stack exhaust system's compute power and make the SSD useless. PureFlash simplify software stack by the following ways:

1. Use RDMA instead of TCP between server nodes and client
1. manage raw SSD directly instead of using file system
1. provide block service only

3. Software design

The whole system include 3 modules (View graph with tabstop=4 and monospaced font)

			   
                                                            +---------------+
                                                            |               |
                                                       +--->+  MetaDB       |
                                                       |    |  (HA DB)      |
                             +------------------+      |    +---------------+
                             |                  +------+
                             | S5conductor      |           +---------------+
                        +---->  (Max 5 nodes)   +----------->               |
                        |    +--------+---------+           | Zookeeper     |
                        |             |                     | (3 nodes)     |
                        |             |                     +------^--------+
+-------------------+   |             |                            |
|                   +---+    +--------v---------+                  |
| S5bd  S5kd        |        |                  |                  |
| (User and kernel  +------->+ S5afs            +------------------+
| space client)     |        | (Max 1024 nodes) |
+-------------------+        +------------------+

3.1 S5afs, S5 All Flash System

This module is the server daemon, provide all data service on store. include:

SSD disk management
Networ interface (RDMA and TCP protocol)
IO handling

There're at most 1024 S5afs nodes in a cluster. All s5afs works in acitve mode, since every s5afs need to provide data service.

3.2 S5conductor

This is the control module to conduct all players in storage cluster. A cluster should has at least 2 s5conductor nodes and at most 5 are supported. S5conductor works in active-standby mode. only one conductor is active. All others in standby.

3.3 Zookeeper

All conductor and afs nodes(instance) register themself to zookeeper, so the active conductor can discovery services in cluster.

3.4 MetaDB

MetaDB is a PostgreSQL cluster with HA.

3.5 S5bd and S5kd

S5bd is user space client. Qemu

networks ports

49162 store node TCP port 49160 store node RDMA port

49180 conductor HTTP port 49181 store node HTTP port

Thanks for:

IntelliJ has provide all develop IDE for Java/C++/golang

zhenshuitieniu/PureFlash