DAS, NAS and SAN

© 2009 IBM Corporation

Statements of IBM future plans and directions are provided for information purposes only. Plans and direction are subject to change without notice.

DAS, NAS and SAN

Ryan LeonardStorage and Solutions Architect


System Storage July 2009

Agenda

DAS, NAS, and SAN

SAN host interfaces– SAS– iSCSI– FC



3 categories of external storage DAS

– Direct-attached storage device– Generally attached / dedicated to a

specific server

NAS– Network-attached storage– Connected to a server via a network– Can be shared or dedicated

SAN– Storage Area Network– Connected to server via a storage

network– Can be shared or dedicated

Server A Server B Server C

JBOD A JBOD B JBOD C

Ethernet


NAS

Ethernet


SAN

Ethernet



Why use either a SAN or NAS?

Why consolidate anything?– Let’s consider an analogy

Greater efficiency

Simplified management

Increased utilization

Reduced cost

Leverage features



NAS detail

NAS– Provides file-level access to storage

• Ethernet connectivity / TCP/IP• CIFS (Common Internet File System)• NFS (Network File System)

– Networked file system allows for concurrent access to data– Several layers between data request and receipt

Server

Data NIC

Storage controllerNAS

NFS/CIFS TCP/IP

HBA

Disk(s)



SAN detail

SAN– Provides block-level access to storage

• Ethernet (iSCSI)• Fibre Channel

– Concurrent access generally not allowed to specific datasets– Remote disk(s) appear as locally attached block devices to server

Server

Data HBA

Storage controller

Disk(s)



Interface Options

Serial attached SCSI (SAS)

iSCSI

Fibre Channel (FC)



SAS – Serial Attached SCSI– A serial communication protocol designed for transfer of SCSI

commands and data to and from devices over point-to-point interconnections

Key Benefits– New roadmap with industry-wide acceptance– Significant performance enhancements

• 3-Gbps SAS x4 “wide” ports– Cost equivalent to parallel SCSI– Freedom from 15 drive maximum per SCSI channel

SAS Basics and Benefits



SAS Special Considerations

Distance limitations – 8 meters per discreet connection

Perceived complexity based on the newness of the technology

SAS expanders, which will support SAN-like capabilities for SAS, are still in development

Limited to the number of servers that can be attached – based on the number of SAS host ports on the storage system



SAS Positioning

Excellent solution for directly attaching one to three local servers to a single storage device– Cost-effectively facilitates one-room storage configurations– Offers outstanding performance – No networking expertise necessary – removes complexity– Low cost and simple to use– High bandwidth and low latency



iSCSI Basics and Benefits

iSCSI - internet Small Computer System Interface– A network protocol that enables transmission of SCSI commands

and data over an IP-based network usually via an Ethernet interface

Key Benefits:– Low cost – Less complexity

• Extensive knowledge base – expertise in every IT organization

– Flexible configuration topologies – Extensive reach with no distance limitations – Future performance

• 1Gb/s today with roadmap for 10Gb/s and beyond



iSCSI Special Considerations

Network congestion risks the dropping of frames – important to evaluate configuration to foresee any bottlenecks

Achievable performance is misunderstood – Hardware and connection parameters can be leveraged to achieve

desired performance

Security at risk when sharing IP storage networks with the existing network– Separate storage traffic from normal LAN traffic

Disparate expertise and confusion over storage and networking IT roles



iSCSI Positioning

Interface of choice for entry-level and SMB storage networks where FC is cost prohibitive– iSCSI has turned the corner, with a large number of installations in

companies of all sizes – Users are growing more familiar with the lower-cost alternative to FC– Reach – IP SANs can to be located virtually anywhere. – Minimal storage investment – utilize existing IP SAN and additional

equipment is relatively inexpensive – Leverage existing IT resources – in-house IP expertise – Simplify installation and management – a mature technology with

proven management tools can be easily facilitated – Extend shared storage benefits to all servers – with minimal

per-server connectivity costs



FC Basics and Benefits FC – Fibre Channel

– A serial networking interface that supports the transmission of upper level protocols – including SCSI command sets and data – over fiber optic or copper cables

Key Benefits – Scalable – supports up to 16 million addresses.– Distance – 10,000 meters maximum cabling length – High bandwidth – low latency and high IOPs– Investment protection – auto-negotiating link speeds allowing for

seamless integration into an existing 1Gb/s or 2 Gb/s environment– Congestion free with credit-based flow control delivering data as fast as

the destination buffer is able to receive it.



FC Special Considerations

Steep learning curve for administrators unfamiliar with deployment and management

Expensive and complex – Costly FC SAN equipment and maintenance – Training personnel internally or hiring a service company is a

significant addition to TCO

Low-cost servers will typically not be included as the investment to attach it can outweigh the cost of the server itself – does not always make financial sense to deploy



Dominates SANs today and expected to retain dominance in the enterprise market – FC will maintain advantages in both performance and scalability– Most mature and time-proven designs– High addressability necessary for large customers with thousands of

servers– Takes the fullest advantage of server clusters

• 4, 8, 16 and up to 100 or more servers as needed– Data integrity – class of service settings guarantees delivery of

frames

FC Positioning



To simplify…

Performance

Scalability Cost

SASFC

iSCSI

Pick 2…



Summary

DAS, NAS, and SAN have intrinsic differences– Cost– Performance– Ease of management

SAS, iSCSI, and FC– Cost vs. scalability vs. performance

Documents

DAS, NAS and SAN