2.4 What is a Storage Array

A storage array is a type of compute system designed to providing storage to externally attached servers through storage network. These storage arrays might be comprised of number of mechanical hard disks (HDD), Solid-state drives (SSD) or both together. In general, a storage array can have petabyte (PB) of storage space which can be allocated to the servers in the network. Storage arrays connect to host computers over a shared network and typically provide advanced reliability and enhanced functionality.

These arrays are designed to provide an optimally cooling airflow, vibration dampening and a clean protected power supply along with providing space to the servers through the storage network. Storage arrays come in three major flavours.

Storage Area Network (SAN)

Network Attached Storage (NAS)

Unified (SAN and NAS)

Also Read: Types of Storage Devices used in Storage Arrays

SAN Storage Arrays also known as block storage arrays provide connectivity through block based protocols such as Fibre Channel (FC), Fibre Channel over Ethernet (FCoE), Internet Small Computer System Interface (iSCSI), or Serial Attached SCSI (SAS). Block storage arrays send low level disk drive access commands called SCSI command descriptor blocks (CDBs) such as READ block, WRITE block and READ CAPACITY over the SAN. SAN storage Arrays are the commonly used arrays in the IT storage market.

Also Read: Introduction to Fibre Channel (FC) SAN Architecture and port virtualization

NAS Storage Arrays also known as FILERS, provide connectivity over file-based protocols such as Network File System (NFS) and SMB/CIFS. File based protocols work at a higher level than low level block commands. They manipulate files and directories with commands which can create files, rename files and close a file etc. It is generally used to consolidate Windows and Linux file servers, where hosts mount exports and shares from the NAS in exactly the same way they would mount an NFS and CIFS share from a Linux or Windows file server. Because NAS protocols operate over shared Ethernet networks, they usually suffer from higher network based latency than SAN storage and are more prone to network related issues. Also, because NAS storage arrays work with files and directories, they have to deal with file permissions, user accounts, Active Directory, Network Information Service (NIS), file locking and other file related techniques.

Also Read: File Based Storage Systems (NAS) Overview

Unified Storage Arrays, also known as multi-protocol arrays provide shared storage over both block and file protocols. IT contains both SSD's and HHD's to combine the advantages of both the disk type techniques, these arrays provide both block and file based storage in a single storage array. Different vendors might implement unified arrays in different ways but the net result is a network storage array that allows storage resources to be accessed by hosts either as block LUNs over block protocols or as network shares over file-sharing protocols.

Also Read: Block Based Storage Systems (SAN) Overview

However, the main purpose of all types of storage arrays (SAN and NAS) is to pool together storage resources and make those resources available to hosts connected over the storage network. These storage arrays also provides the following advanced features and functionalities

Replication

Snapshots

Offloads

High Availability and resiliency

High Performance

Space efficiency

Types of Storage Arrays

Most storage vendors offers two types of storage arrays, enterprise-class arrays and midrange arrays. In general, enterprise-class arrays offers grid-based architecture and midrange arrays offers dual-controller architectures.

Also Read: Unified Storage Systems Overview

Dual-Controller architectures provide many of the advanced features seen in enterprise-class grid architectures but at a cheaper cost. Dual-controller architectures are also limited in scalability and do not deal with hardware failures. Grid-architectures offer scale-out and deal better with hardware failures but with additional cost.

Enterprise-Class Storage Arrays offer

Multiple controllers

Minimal impact when controllers fail

Online non-disruptive upgrades (NDUs)

Scale to over 1,000 drives

High Availability

High Performance

Scalable

Always on

Predictable Performance

Expensive

Midrange Storage Arrays offers dual-control architectures and also provides the high

Performance

Scalability

Availability

All-Flash Arrays

These arrays contains all flash drives and the main purpose of this type is to increase the performance compared to traditional storage arrays. They have front-end ports, usually some DRAM cache, internal buses, backend drives, and the like. They take flash drives, pool them together, carve them into volumes, and protect them via RAID or some other similar protection techniques. Many even offer snapshot and replication services, thin provisioning, deduplication, and compression. All-flash arrays can be dual-controller, single-controller, or scale-out.

Advantages of Storage Arrays

Storage arrays allows storage administrators to pool storage resources, thereby making more-efficient use of both capacity and performance. Some of the advantages of storage arrays are

Increased capacity by pooling all the disk storage

Increased Performance by pooling all the IOPS

Easy and simplified management of disk space

Advanced functionalities which offer advanced features such as replication, snapshots, thin provisioning, deduplication, compression, high availability, and OS/hypervisor offloads.