Definition: A storage area network (SAN) is a type of local area network (LAN) designed to handle large data transfers. A SAN typically supports data storage, retrieval and replication on business networks using high-end servers, multiple disk arrays and Fibre Channel interconnection technology.
SAN technology is similar but distinct from network attached storage (NAS) technology. While SANs traditionally employ low-level network protocols for transfering disk blocks, a NAS device typically works over TCP/IP and can be integrated fairly easily into home computer networks.
The term SAN can sometimes refer to system area networks instead of a storage area network. System area networks are clusters of high performance computers used for distributed processing applications requiring fast local network performance. Storage area networks, on the other, are designed specifically for data management.
What is a SAN topology?
SAN is a Fibber Channel network architecture with multiple hosts (computers) and one or more Storage chassis. Storage is directly addressable from any host on the networks.
What is a SAN management software?
Take a simple case, one Storage chassis talking to one host, the chassis react exactly like a Computer disk, data are addressable thanks to a FAT (File Allocation Table) managing file locations, read / write rights and keeping data integrity. If you have this case, the Host operating system is able to handle this host/Storage case.
Now imagine, five hosts reading and writing on ONE Storage chassis. The File system would fall in part at the first start, just because FATs on Windows, Unix or MAC are not designed to handle MULTIPLE Hosts.
Here comes the Sharing software, it is an AGENT who's job is to protect the FAT and manage read and write I/o. This software lives in back ground of the operating system and most of the time is invisible to the user. Each machine connected to the SAN have one sharing software license running. At every request user makes for access, creating or deletion of a file located in one of a SAN partition, The sharing software will inform all other Agents of the performed task. We can summarize by saying that sharing software duplicates the SAN FATs and create a "VIRTUAL FATs" over Host members, and before accessing a file it updates VIRTUAL FAT to insure data integrity.
What is SAN Meta Data?
This Virtual FAT need to communicate across network, because Fibber Channel is designed to move large files and is not very responsive with small one, Sharing software are using Ethernet protocol to exchange information to update the V-FAT. This is called Meta Data (MDT)
Choosing the right Sharing software
They are a number of sharing software, first we can classify them in two; File level and Volume Level,
Volume level are the first generation of SAN, once a host raised writing requirement on a particular volume, all other members can only read this volume. This system do not require MTD locking is performed directly via Fiber Channel networks. (ATTO ACCELWARE)
File level sharing is the most advanced packages the locking is not on Volumes but in files, so any host can access any file, simultaneously or not with others. When a host creates or update a file, it is locked, and other hosts can not write in it. This file access is very flexible.
I qualified : MetaSan, ADIC
NAS was developed to address problems with direct attached storage, which included the effort required to administer and maintain “server farms”,and the lack of scalability, reliability, availability, and performance.