Adaptec 5325301808-6 Datasheet download pdf (Page 15)

QL S

RVER

000

CSI S

RVER

™

8000 C

ARACTERIZATION

Figure 6 - iSCSI Protocol Stack Layers

The initiator (usually a server) makes the application requests.

These are converted (by the SCSI class driver) to SCSI com-

mands, which are transported in command description blocks

(CDBs). At the iSCSI protocol layer, the SCSI CDBs (under

control of the iSCSI device driver) are packaged in a protocol

data unit (PDU) which now carries additional information,

including the Logical Unit Number (LUN) of the destination

device. The PDU is passed on to TCP/IP. TCP encapsulates the

PDU and passes it to IP, which adds the routing address of the

final device destination. Finally, the network layer (typically

Ethernet) adds information and sends the packet across the

physical network to the target storage device.

5.5 Microsoft Windows iSCSI Initiator Service

The initiator service enables the host computer system to dis-

cover target storage devices on the storage area network and to

determine whether or not it has access to those devices. The

iSCSI Naming Services (iSNS) client—the code required to

interact with the iSNS server—is built directly into the initia-

tor service, enabling the initiator service to maintain a list of

targets reported via the iSNS server as changes are made to

iSCSI v

umes on the Snap Server™ 18000.

6. Conclusion

Initially, Network Attached Storage (NAS) were used for file-

based storage that could be shared with Windows clients, Unix

lie

nts,

and

ple Macintosh clients easily and cost-effectively.

t that t

ime,

the

e w

e two popular storage choices for

Microsoft® SQL Server™ 2000 database storage: 1) Direct

tta

ched Storage (DAS) using SCSI- based server integrated

AID ar

y controllers or PCI RAID array controllers with

SCSI-based storage enclosures or, 2) Storage Area Network

(SAN) using Fibre Channel. To implement DAS for

Microsoft® SQL Server™ 2000 storage is relatively easy, moder-

ately priced, performs well, but is very inflexible and can be a

maint

nanc

e c

hal

lenge when there are many servers each with

their own DAS. For customers who want to migrate to a con-

solidated storage environment to overcome the inflexibility

and maintenance issues of DAS, SAN was the answer. While

SAN’s are the most redundant and the fastest storage available,

hey are also the most costly and the most complicated to

implement. This was all before iSCSI however.

iSCSI-based NAS bring to market a third option. To imple-

ment a Microsoft® SQL Server™ 2000 with a NAS using iSCSI

is very easy, flexible, inexpensive, and allows the organization

to move to a consolidated storage approach. The downside to

implementing iSCSI is performance. All data packets have to

travel over the network, which for most organizations is Ether-

net. Further improvements to Ethernet in the future will help.

However, the performance numbers from the tests were good

as compared to DAS (difference drive throughput on a 3.5 mil-

lion row select between the DAS and a iSCSI solution was

3.23MB/s), and may prove suitable for many organizations.

This is especially true, for organizations that are trying to

reduce TCO in their storage strategy or cannot afford the large

upfront and ongoing maintenance expense of a SAN solution.

There has been a lot of energy and excitement about iSCSI,

and it appears that iSCSI is finally coming to fruition after a

few slow years of development. Microsoft released its software

iSCSI initiator in June 2003. A few months later, Microsoft

awarded its iSCSI Designed for Windows logo to several ven-

dors, some with iSCSI initiators and some with iSCSI targets.

Adaptec has been awarded the Designed for Windows logo on

several of their products, making them ideal for storing

Microsoft® SQL Server™ 2000 data.

Interlink’s testing validates that the Adaptec Snap Server iSCSI

device is a viable alternative as a storage solution in Microsoft®

SQL S

er™ 2000 environments. Is it time for you to evaluate

iSCSI f

r y

our st

orage needs? For those companies that might

still be looking to replace older DAS storage, or have avoided

moving to SAN technology due to high cost and complexity,

Snap Server iSCSI devices should definitely be considered.

Application

Ethernet

TCP/ IP

iSCSI protocol

CSI

Logical Unit

TargetInitiator

TCP /IP

iSCSI Protocol

CSI

Ethernet

Network

P/N 666766-011 Printed in USA. 02/05 3702_1.1

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