Low Cost SAN

Version No.: 1

Date: 25/04/2009

Revision History

Version No.


   Prepared by 

Significant Changes




       Krishna Kumar
       (NEC HCL ST)

1 Objective

The objective of this document is to provide making of Low Cost SAN using FOSS tools. We have tried to set up a SAN which has following features:

•  Low cost and easily affordable

•  Ensured Scalability

•  High Reliability

•  Easily Manageable

•  High Performance

•  Ensured Security

•  High availability

2  Definitions, Acronyms and Abbreviations

This section provides a list of all definitions, acronyms and terms required to properly interpret this document as well as to understand SAN terms and terminology.




ATA over Ethernet, a open storage protocol


Advance Technology Attachment


End Point of communication ( normally refers to server side )


A host that requests access to storage device ( client end )


Red Hat Clustering Suite


A signal periodically sent out by a hardware component in order to inform another component that it is working normally


Internet Small Computer System Interface


Serial ATA, a newer version of ATA interface


Global File System, a cluster aware filesystem for Linux


Storage Area Networking


Logical Volume Manager


Redundant Array of Inexpensive disks


Distributed Replicated Block Device


Network Block Device


Enhanced Network Block Device


Global Network Block Device


High Availability, a clustering solution for Linux which provides reliability, availability and serviceability


Free Open Source Software


Distributed File System for Windows


Linux Virtual Server

3  References

This section tells all the references and urls used to prepare this document.
















http://www.redhat.com/docs/manuals/enterprise/RHEL-5-manual/Cluster Administration/


4  Layered Architecture of SAN

4.1  Brief Description and Layered Architecture

This is the investigation document which touches each aspect of Low Cost SAN making right from hardware, OS and Softwares. The layered architecture of our SAN is shown in following diagrams.

Server Architecture:

Client Architecture:

In this diagram, three boxes in red color depicts the solution for windows and DFS is Microsoft distributed file system for windows server.


4.2  SAN Features and available options

Having above architecture in mind we have tried to achieve all the features of low cost SAN in terms of speed, reliability, security, scalability and availability. Following table gives us an overview against the features and corresponding available options. All the softwares which we have used to achieve SAN features are available on FOSS:

SAN Features

Available Options On FOSS

Low Cost & Simplicity

AoE Protocol and corresponding softwares are available on FOSS.


No routability provides inherent security

Speed of ATA disk

1) Typical 7200-rpm SATA disk drive: 105 MB/s (sustained throughput)

2) Typical 7200-rpm PATA disk drive: 72 MB/s (sustained throughput)

Speed of Ethernet

1) Gigabit Ethernet (1000baseT): 125 MB/s

2)10-Gigabit Ethernet: 1,250 MB/s

Data Packets

AoE simply delivers 48 bytes and data ( only extra 48 bytes )

Full Virtualization Support

Fully Compatible with hypervisors such as Xen, VMware, Microsoft Virtual PC to virtualize computers that are used as servers

Virtualized disk

We can combine multiple 22 TB disk into a single RAID disk.

Device access through Internet

Remote access to an AoE device through the Internet can be achieved

through tunneling, we can use software to convert local packets into routable packets at both ends of a link.

Easy management of AoE Servers and nodes

AoE Tools like CEC provides a terminal interface for AoE device. All the clusters and nodes can also be managed by RHCS cluster manager

Connecting Multiple Disks

24 port SATA controller PCI express card having capacity >=2TB per disk

Theoretical limits of AoE devices

AoE has a limitation of 65535 major x 255 minor addresses, so you're
limited to approximately 16 million block devices on a single
broadcast domain / san. For each individual block device, the ATA
lba48 addressing restricts you to about 140 PetaBytes.

Diskless booting Support

Diskless booting (PXE booting) is available in AoE for windows as well as for Linux


RHCS fencing daemon provide fencing against corresponding failover domains

Network Load balancing

RHCS lvs and piranha provides network load balancing

Proper Synchronization among all the nodes

RHCS GFS/GFS2 uses DLM to provide this feature

Block Level Redundancy

DRBD is a tool available on Foss to provide high availability in SAN in terms of block level. If DRBD is used with heartbeat and rhcs, it's a very good solution for HA in storage networking.

Directory level Redundancy

NFS fail over and auto mounting is easily handled by RHCS.

Resource Management and ensured communication among other nodes

CMAN of RHCS and Heartbeat are good solutions against this.

4.3  Overview of SAN with HA/Failover

The main challenge of a reliable SAN is high availability and zero down time. Thanks to the tools like LVS, RHCS, HEARTBEAT and DRBD by which we can easily restart our applications and can do migration of services. Following diagram shows the failover a node and relocation of services, so that users get their applications running even if corresponding node crashed.

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