IP Storage: What Lies Beyond

DQC News Bureau
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IP storage infrastructure meets technical

requirements of traditional SAN at reduced performance levels.


IP storage is a new technology area that is fast evolving to become an

industry standard with increasing support from industry leaders like Microsoft,

Cisco, and EMC. IP storage leverages on Internet SCSI (iSCSI) protocol for

networking the storage devices and host systems. iSCSI encapsulates SCSI

commands into IP packets and transmits them over IP networks.


means that standard IP networks can be used for building storage networks to

connect storage devices and host servers that technically meet the requirements

of a fibre channel storage area network (SAN). These IP SANs leverage standard

network infrastructure components.

Types of storage

NAS: NAS connects to the local area network (LAN) infrastructure through

Gigabit, Fast Ethernet or ATM technologies. NAS enables client systems on the

network to access storage at the file level using remote file access protocols

such as Network File System (NFS) and Common Internet File System (CIFS).


FC SAN: From the connectivity perspective, fibre channel is flexible almost

like a general communication network and has low protocol overheads similar to

SCSI or ESCON. Fibre channel supports transporting protocols such as IP, HIPPI

or SCSI etc.

In a FC SAN, fibre channel transports SCSI over the network connecting hosts

and storage devices. Host servers connecting storage devices therefore will

access storage at SCSI block level.



Over the last decade both NAS and FC SAN technologies have matured and now

support a wide range of operating systems and applications. However, both these

technologies serve two different technological requirements and remain

complementary to each other. FC SAN is definitely an expensive infrastructure

that requires fibre channel host bus adapters, cabling, and switches in addition

to the storage devices themselves.

Flexibility, low cost, availability of higher bandwidth, and ability to

transport different types of data have made IP networks an attractive option for

building storage networks. iSCSI supported storage devices allow hosts to access

storage resources at block level as in a traditional FC SAN.

From the hardware connectivity perspective both NAS and iSCSI resemble each

other. Both storage devices connect to the IP network. The difference is in the

level at which the host systems access the storage — file level in case of NAS

and block level in case of iSCSI.


It is important to note that unlike NAS and FC SAN, there are only a limited

number of operating systems that support iSCSI. Hence, while looking at iSCSI as

a cost effective option against FC SAN, support for various operating systems in

the environment needs to be assessed.

IP storage Deployment scenarios

Storage on IP is possible in several permutations.

a) Simple IP SAN: A conceptual layout of iSCSI storage network is

shown in the figure. Host systems are connected to the IP storage device using

standard local area network infrastructure.


In figure 1.1, it can be noted that application performance will be greatly

affected due to the protocol overhead inherent to IP networks. The host bus

adapters connecting host servers to IP storage or the host operating system

needs to take care about encapsulation of SCSI commands to transmit through IP


Network adapters with TCP off-load engine ensures that the operating systems

are not loaded with the responsibility of protocol conversions. In IP SAN,

overall performance can be improved using host bus adapters with TCP off-load



IP Storage is typically used in consolidating application servers that

require low performance block level access to the storage device.

 b) IP SAN and FC SAN on common fibre channel storage: As shown

in figure 1.2, iSCSI can also be used in requirements where fibre channel SAN

and IP SAN needs to co-exist. The figure illustrates building Fibre Channel SAN

and IP SAN on a single Fibre Channel Storage System. In order to consolidate IP

SAN and FC SAN on a single fibre channel storage system, FC to IP gateways are

used as indicated in the figure 1.2.

 c) Data replication over WAN link: Another deployment of iSCSI

is to perform data replication from one fibre channel storage system to another

as a means for disaster recovery (as shown in figure 1.3). When the disaster

recovery site is thousands of miles away from the primary site, using fibre

channel links for data replication across storage systems is not feasible. iSCSI

helps using WAN infrastructure to perform block level replication of data across

the two locations. Source volumes from primary storage system can be replicated

to target volumes in a secondary storage system over WAN links as indicated in

figure 1.3 below.


 IP storage can be ideal in software houses for application development

and testing especially in database environments. Database environments will

typically require direct attached storage for hosting databases.

 IP storage can be deployed in research & development organisations

to build large IP SANs cost-effectively. The primary storage infrastructure

requirement of research organisations and development houses is to satisfy their

technical needs and performance is not a major concern. IP storage

infrastructure meets technical requirements of traditional SAN at reduced

performance levels.


iSCSI as a storage networking technology will evolve further to support a
variety of operating systems and applications. There will be a performance

difference between traditional fibre channel SAN and IP SAN while both these

technologies will continue to scale to support higher bandwidths. Storage

networking will use all the three key technologies — NAS, FC SAN and IP SAN to

support requirements of various applications and also to optimise the storage

networking cost.

Arun Rao is Head-Storage Solutions at Datacraft India.