What is DAS, SAN, NAS and Unified Storage..??

DAS: Direct-Attached Storage

      Direct-attached storage (DAS) is digital storage directly attached to the computer accessing it, as opposed to storage accessed over a computer network. Examples of DAS include hard drives, optical disc drives, and storage on external drives.

Direct-Attach Storage connectivity example

In Above Screen it shows that Storage device is directly attached to Server it means in real

Example: If you attach a External USB drive to your Server/Desktop it is best example for DAS.

Same as above example, we can attach SCSI and SAS Storage Devices such as HDD and RAID Controllers.


  • An initial investment in a server with built in storage can meet the needs of a small organization for a period of time. But as data is added and the need for storage capacity increases, the server has to be taken out of service to add additional drives.
  • DAS expansion generally requires the expertise of an IT professional, which means either staffing someone or taking on the expense of a consultant.
  • A key disadvantage of DAS storage is its limited scalability.
  • A Host Bus Adapter can only support a limited number of drives. For environments with stringent up time requirements, or for environments with rapidly increasing storage requirements, DAS may not be the right choice.

  • One advantage of DAS storage is its low initial cost.

 SAN: Storage Area Network

              SAN (storage area network) is a high-speed network of storage devices that also connects those storage devices with servers. It provides block-level storage that can be accessed by the applications running on any networked servers. SAN storage devices can include tape libraries and disk-based devices, like RAID hardware.

 Block level access means, server can able to create its own file system on SAN disk with mapped to server.
Storage Area Network Connectivity Example


  •     SAN Architecture facilitates scalability - Any number of storage devices can be added to store hundreds of terabytes.
  •     SAN reduces down time - We can upgrade our SAN, replace defective drives, backup our data without taking any servers offline. A well-configured SAN with mirroring and redundant servers can bring zero downtime.

  •     Sharing SAN is possible - As SAN is not directly attached with any particular server or network, a SAN can be shared by all

  •     SAN provides long distance connectivity - With Fibre channel capable of running upto 10 kilometers, we can keep our data in a remote, physically secure location.  Fibre channel switching also makes it very easy to establish private connections with other SANs for mirroring, backup, or maintenance.

  •     SAN is truly versatile - A SAN can be single entity, a master grouping of several SANs and can include SANs in remote locations.

  •     SANs are very expensive as Fibre channel technology.

  •     Leveraging of existing technology investments tends to be much difficult. Though SAN facilitates to make use of already existing legacy storage, lack of SAN-building skills has greatly diminished deployment of homegrown SANs.

  •     Management of SAN systems has proved to be a real tough one due to various reasons. Also for some, having a SAN storage facility seems to be wasteful one.
  •     Also, there are a few SAN product vendors due to its very high price and very few mega enterprises need SAN set up.

NAS: Network Attached Storage

    Network-attached storage (NAS) is a type of dedicated file storage device that provides local-area network local area network (LAN) nodes with file-based shared storage through a standard Ethernet connection.
Network Attached Storage Example

     NAS devices, which typically do not have a keyboard or display, are configured and managed with a Web-based utility program. Each NAS resides on the LAN as an independent network node and has its own IP address.


  •     NAS systems stores data as files and support both CIFS and NFS protocols. They can be accessed easily over the commonly used TCP/IP Ethernet based networks and support multiple users connecting to it simultaneously.
  •     Entry level NAS systems are quite inexpensive – they can be purchased for capacities as low as 1 or 2 TB with just two disks. This enables them to be deployed with Small and Medium Business (SMB) networks easily.
  •     A NAS device may support one or more RAID levels to make sure that individual disk failures do not result in loss of data.
  •     A NAS appliance comes with a GUI based web based management console and hence can be centrally accessed and administered from remote locations over the TCP/IP networks including Internet/ VPN / Leased Lines etc.
  •     NAS appliances are connected to the Ethernet network. Hence servers accessing them can also be connected to the Ethernet network. So, unlike SAN systems, there is no need for expensive HBA adapters or specialized switches for storage or specialized skills required to set up and maintain the NAS systems. With NAS, its simple and easy.
  •     Ethernet networks are scaling up to support higher throughputs – Currently 1 GE and 10GE throughputs are possible. NAS systems are also capable of supporting such high throughputs as they use the Ethernet based networks and TCP/IP protocol to transport data.
  •     The management tools required to manage the Ethernet network are well established and hence no separate training is required for setting up and maintaining a separate network for storage unlike SAN systems.


  •     Transaction intensive databases, ERP, CRM systems and such high performance oriented data are better off when stored in SAN (Storage Area Network) than NAS as the former creates a network that has low latencies, reliable, lossless and faster.Also, for large, heterogeneous block data transfers SAN might be more appropriate.
  •     At the end of the day, NAS appliances are going to share the network with their computing counterparts and hence the NAS solution consumes more bandwidth from the TCP/IP network. Also, the performance of the remotely hosted NAS will depend upon the amount of bandwidth available for Wide Area Networks and again the bandwidth is shared with computing devices. So, WAN optimization needs to be performed for deploying NAS solutions remotely in limited bandwidth scenarios.
  •     Ethernet is a lossy environment, which means packet drops and network congestion are inevitable. So, the performance and architecture of the IP networks are very important for effective high volume NAS solution implementation at least till the lossless Ethernet framework is implemented.
  •     For techniques like Continuous Data Protection, taking frequent Disk Snapshots for backup etc, block level storage with techniques like Data De-duplication as available with SAN might be more efficient than NAS.
  •     Sometimes, the IP network might get congested if operations like huge data back up is done during business hours.

Unified Storage

     Unified storage is a storage system that makes it possible to run and manage files and applications from a single device. To this end, a unified storage system consolidates file-based and block-based access in a single storage platform and supports fibre channel SAN, IP-based SAN (iSCSI), and NAS.

 It means combined of NAS and SAN is called as unified Storage.
Example for unified Storage Diagram

Come Back to NetApp Storage environment is Unified Storage Devices.

In NetApp Storage We have below mentioned series of models are available.

FAS: Fiber Attached Storage

V-Series: Virtualization Series, this Series is used most of times to virtulize the SAN with other SAN devices. To Reduce the cost in real terms.

E-Series:      The E-Series is NetApp's name for new platforms resulting from the acquisition of Engenio. Aimed at the storage stress resulting from high-performance computing (HPC) applications, NetApp offers full-motion video storage built on the E-Series Platform that enables, for example, government agencies to take advantage of full-motion video and improve battlefield intelligence. Additionally, NetApp offers a Hadoop Storage Solution on the E-Series that is designed to enable real-time or near-real-time data analysis of larger and more complex datasets.

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