A SAN is a block storage method in which storage devices are connected to hosts via a high-speed network to share data between clients, servers, and storage. A popular solution in data centers and large companies due to high flexibility, performance, reliability and scalability.
The unique features, advantages, and disadvantages of SANs
- Fixed block size: Suppose a new merchandiser sorted the books by volume and put the same books on the shelf - 400 pages each (or data blocks of 4 kilobytes each). In a SAN, data blocks can be organized into groups of different sizes for more efficient management and storage. For small files, small blocks are more effective - and vice versa.
- Variable block size: The merchandiser was told that no one chooses books by size, so he sorted the books by author and put the case on the shelf. The volume of books now ranges from 200 to 1200 pages (variable data block size). In a SAN, you can organize variable size blocks of data.
- Data in blocks: The content of the book is important to the buyer, not the order in which they are placed on the shelves. If he needs a new Stephen King novel, he will look for it, not Pelevin's books. For applications and the SAN operating system, it is the data in the blocks that matters, not how they are physically located on the storage devices.
- Independent access to data: The buyer can select any book (block of data) on the shelf independently of others. In SAN, data blocks can be accessed independently of each other - so the application gets direct and fast access to the required information.
- SAN management: Merchandiser analyzes sales through the accounting system and changes the layout of the books to increase sales. He adds new ones, sends the old ones to the warehouse, moves the most popular books to prominent places and hides the unpopular ones. In a SAN, the sysadmin and the OS can similarly manage data blocks in response to changes in data storage needs.
Advantages of SAN:
- Block storage and shared access: Direct low-level access to data is possible without unnecessary abstractions, such as file systems. SAN is focused on shared access of servers and users to their resources (to storage resources).
- High performance: SAN gives excellent performance and fast access to data (thanks to Fiber Channel or iSCSI). Therefore, it is great for demanding applications such as databases and virtualization.
- Reliability and fault tolerance: SAN can implement fault tolerance mechanisms at the hardware level (duplication of components), at the software-hardware level (geo-distribution, clustering, RAID, intelligent routing systems) and at the network level (multichannel, network channel redundancy, end-to-end access). It is possible to achieve almost 100% availability 24/7/365, but only the Sith reduce everything to an absolute
- Flexibility and scalability: A SAN allows you to easily expand storage, add new devices, and/or scale out old ones.
- Centralized management: A huge SAN can be managed centrally - without physical access to individual network nodes.
Disadvantages of SAN:
- Costs and complexity: If you are not deterred by the cost of software, equipment and maintenance, then wait for the search and hiring of qualified specialists, deployment and administration.
- SPoF, aka single point of failure: SANs are fault-tolerant, but there is a risk of creating an SPoF. For example, access to the SAN management center through a single backbone provider.
- Network Dependency: Problems in the network (and its nodes) can and will affect SAN performance and availability.
- Redundancy: Sometimes SANs grow so large that the architecture becomes too complex and the data to back up is too much.
Examples of SAN usage:
- Large enterprises: In large corporate environments where hundreds of servers and users need high-speed and centralized data storage.
- High-load databases (DBs): SANs provide fast access to data for mission-critical databases, bringing business process efficiency to a new level. Plus backup and fast recovery.
- Virtualization: SAN is the basis of large virtualized environments (for example, VMware or Hyper-V), where migration of virtual machines and load distribution are very important. Data sharing, centralized management and high data availability are also indispensable.
- Hyperconverged infrastructures (HCI): In infrastructures where data storage, computing resources, and network functions are combined into a single platform, the SAN can create separate storage for specific applications, while the HCI is used for general computing tasks and storage.
- Working with virtual desktops (VDI): When virtualizing desktops, where many clients access a centralized block storage, SAN provides fast and reliable access, as well as redundancy and storage optimization.
SAN components
A SAN consists of several key components, including storage systems (typically hard disk arrays), switches, and server adapters.
- Repositories: Physical devices for data storage. These can be servers, disk shelves, DAS and SZD. There is such a thing - Unified Storage, when storage devices can simultaneously store data in block and file form, useful if you use SAN and NAS at the same time.
- Hosts: Servers or other devices that connect to the SAN to access data. Hosts can be physical devices or virtual machines.
- Host Bus Adapters (HBAs): These are physical adapters that connect to the host (usually via PCIe). The HBA provides an interface to connect the host to the SAN using various protocols: Fiber Channel, iSCSI, or FCoE.
- Switches: Switches connect devices in a SAN. Something like intermediaries between hosts and data stores. In small networks there may be one switch, in branched and complex networks there may be dozens.
- Cables and connectors: Patch cords and other cables for connecting servers, switches and SZD.
- Uninterruptible Power Supplies (UPS): Devices like an uninterruptible power supply (but there are much more complex ones, for example, diesel generators) that power the infrastructure in the event of a shutdown of the main power supply.
- Cooling systems: Guarantee the optimal temperature of the equipment. Most often these are split systems.
- Data protection systems: Hardware storage and programs for data security and preservation. For example backup, mirroring, snapshots and data replication.
- Management and monitoring modules: Software or hardware components for SAN management and monitoring. The administrator gets centralized control, performance monitoring and network health analysis.
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