Directly Attached Storage (DAS), Network Attached Storage (NAS), and Storage Area Networks(SAN)

1. Overview

2. Description

Storage Feature	DAS	NAS	SAN
Full Name	Directly Attached Storage	Network Attached Storage	Storage Area Networks
Terminology	A traditional way of storage system Physically connected to a single host machine	Shares network bandwidth User can access at file level over a LAN, a WAN, or over the Internet	Shares data at block level Commonly associated with Fibre Channel networks
Components	Application server, Storage	Application server, File server, Storage	Application server, Storage
Interface Technologies	IDE(PATA, SATA), SCSI(SCSI, SAS)	TCP/IP(Ethernet)	Fibre Channel Switch FCP, iSCSI, FCoE, FCIP, InfiniBand, HyperSCSI, FICON
File System	NTFS, FAT, JFS, HFS, UFS, UDF	NFS, SMB / CIFS	OS / Application decides
Speed of accessing storage	Fast(Channel speed)	Somewhat slow(Channel speed + LAN speed)	Not limited(Channel speed, Expandable)
Ease of adding storage	Might require shutting down servers to add storage	Easy(Hot - Swap)	Easy(Hot - Swap)
Redundant connectivity	No	No	Yes
Centralized management	No	No	Yes
Able to share File System	No	Yes	No
Ease of expansion	Limited to host's physical ports	Allow modestly expansion	Quick and sasy
Suited for databases	Yes	No	Yes
Cost	In expensive	Moderately expensive	Moderately expensive
Distance between server and storage	Must be close under(6 feet)	Distance doesn't matter	Distance doesn't matter
Backup	Each volume copied separately from a server tape	Each volume copied separately from a server tape	Can backup multiple volumes without server interaction
Major Player	Seagate Technologies	NetApp, EMC Corp	Brocade(SAN Equipments), EMC(Storage Equipments)
Best Fit	Local OS	Flat File, Simple data changes	I/Op Intensive, quick block changes, Databases
Who should use	Small and Predictable Storage	Data Backup Simple Extra Storage	Bandwidth Intensive Mission Critical Data
Things to consider	Difficult to Maintain No Load balance	Primally targeted at storing files, not blocks	Price Point
Good	No Network or External Arrays needed Fast Through-Put	Flat File Storage Simple to configure and maintain	Moving Large Blocks of Data Scalable, Reliable, Ease of Management
Additional Advantages	Simpler to setup and configure over NAS/SAN Cheaper than NAS/SAN in terms of raw storage Networks not necessary, doesn't use IP address Faster, more performant and better latency over SAN/NAS Easier to deal with overall considering all things	Enonomical way to provide large storage to many persons or computers Several times easier to setup and configure versus SAN Easy way to provide RAID redundancy to a mass amount of users Allows users permissions, folder privileges, restricted access to documents, etc Higher utilization of storage resources	Economics of scale similar to that of NAS Higher hardware utilization, similar to that of NAS Speed similar or comparable of DAS Allows virtual environments, cloud computing, etc.
Additional Disadvantages	Dedicated resource to a single computer No economies of scale in sharing the storage Can't manage DAS via a network Requires a special hardware connection	Requires IP Address(es) and takes up network space Slower latency and potentially maximum data-transfer issues Performance can be affected by network status	Performance affected by other SAN users Performance limited by a network if configured incorrectly Better performance will still be found using DAS hardware Requires multiple static IP Addresses Generally consumes more IP addresses than NAS devices Complex networking planning is necessary May want to implement virtual networks / different subnets Physical network wiring may affect performance Physical network wiring should be thoroughly planned Generally more expensive than NAS or DAS

 

2.1 Communication Model

2.1.1 DAS

DAS is a traditional direct-attached storage model with dedicated storage resources for each server, with backup over the LAN.

2.1.2 NAS

A typical NAS solution where all traffic flows over the production LAN.

2.1.3 SAN

A basic SAN infrastructure using LAN-free data backup to reduce network traffic, and consolidated storage for scalable storage management.

3. References

https://www.slideshare.net/sagaroceanic11/introduction-to-san-storage-area-networks

https://www.backblaze.com/blog/whats-the-diff-nas-vs-san/

https://www.techopedia.com/definition/29305/network-redundancy

https://blog.oneringnetworks.com/the-need-for-your-business-to-have-a-redundant-internet-connection

https://leapfrogservices.com/redundant-connectivity-how-to-protect-always-on-internet-at-your-business/

https://content.personalfinancelab.com/finance-knowledge/management/centralized-and-decentralized-management-explained/

https://www.open-e.com/solutions/article/solutions-for-data-storage-management-and-centralization/

https://www.petri.com/das-nas-san-storage-technologies

https://en.wikipedia.org/wiki/Network-attached_storage

https://vanillavideo.com/blog/2014/started-storage-understanding-san-nas-das

https://www.how2shout.com/what-is/san-vs-nas-vs-das-explained-compared-which-one-is-the-best.html

https://netappnotesark.blogspot.com/p/blog-page.html

https://www.vita.virginia.gov/media/vitavirginiagov/it-governance/ea/pdf/Boot-via-SAN__vs__Boot-via-DASD__Technical-Brief.pdf