What Is a Storage Array?

              A storage array is a computer system designed for and dedicated to providing storage to externally attached computers, usually via a storage network. This storage has traditionally been spinning disk, but we are seeing an increasing number of solid-state media in storage arrays. It is not uncommon for a large storage array to have more than a petabyte (PB) of storage.
Storage arrays connect to host computers over a shared network and typically provide advanced reliability and enhanced functionality. Storage arrays come in three major flavors:
■■ SAN
■■ NAS
■■ Unified (SAN and NAS)
SAN storage arrays, sometimes referred to as block storage arrays, provide connectivity via 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.
NAS storage arrays, sometimes called 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 that do things such as create files, rename files, lock a byte range within a file, close a file, and so on.

Unified storage arrays, sometimes referred to as multiprotocol arrays, provide shared
storage over both block and file protocols. The best of both worlds, right? Sometimes, and
sometimes not.
The purpose of all storage arrays, SAN and NAS, is to pool together storage resources
and make those resources available to hosts connected over the storage network. Over and
above this, most storage arrays provide the following advanced features and functionality:
■■ Replication
■■ Snapshots
■■ Offloads
■■ High availability and resiliency
■■ High performance
■■ Space efficiency
While there are all kinds of storage arrays, it is a nonfunctional goal of every storage
array to provide the ultimate environment and ecosystem for disk drives and solid-state
drives to survive and thrive. These arrays are designed and finely tuned to provide an optimally
cooling airflow, vibration dampening, and a clean protected power supply, as well as
performing tasks such as regular scrubbing of disks and other health checking. Basically, if
you were a disk drive, you would want to live in a storage array! 


NAS Storage
NAS storage arrays work with files rather than blocks. These arrays provide connectivity
via TCP/IP-based file-sharing protocols such as NFS and SMB/CIFS. They are often 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 or CIFS share from a Linux or
Windows file server. Because of this, hosts know that these exports and shares are not local
volumes, meaning there is no need to write a filesystem to the mounted volume, as this is
the job of the NAS array.
A Windows host wanting to map an SMB/CIFS share from a NAS array will do so in
exactly the same way as it would map a share from a Windows file server by using a Universal
Naming Convention (UNC) path such as \\legendary-file-server\shares\tech.
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 technologies. One common challenge is integrating virus
checking with NAS storage. There is no doubt about it: NAS storage is an entirely different
beast than SAN storage.
NAS arrays are often referred to using the NetApp term filers, so it would not be uncommon
to hear somebody say, “We’re upgrading the code on the production filers this weekend.”
NAS controllers are often referred to as heads or NAS heads. So a statement such as,
“The vendor is on site replacing a failed head on the New York NAS” refers to replacing a
failed NAS controller.
NAS arrays have historically been viewed as cheaper and lower performance than SAN
arrays. This is not necessarily the case. In fact, because NAS arrays own and understand
the underlying filesystem in use on an exported volume, and therefore understand files and
metadata, they can often have the upper hand over SAN arrays. As with most things, you
can buy cheap, low-performance NAS devices, or you can dig a little deeper and buy expensive,
high-performance NAS. Of course, most vendors will tell you that their NAS devices
are low cost and high performance. Just be sure you know what you are buying before you

part with your company’s hard-earned cash.