In-Depth
SAN and NAS: The Convergence of Data and Storage Sharing
SAN and NAS: The Convergence of Data and Storage Sharing
By Greg Schulz
A lot has been written, and debated, about SAN vs. NAS. The debate centers on how one (SAN or NAS) is better than the other, along with Fibre Channel vs. Gigabit Ethernet. While vendors of SAN and NAS products position themselves in an attempt to gain or protect market share, the potential user is left to sift through the confusing messages.
Rather then debate SAN or NAS let's look at how SAN and NAS, along with Fibre Channel and Gigabit (or other networks) can be used to solve business issues in a complementary manner. While implementation and current capabilities differ, both SAN and NAS share common objectives including storage sharing by multiple host or client systems, using network or network like interfaces as opposed to dedicated and direct attached storage mechanisms, and simplified management to reduce costs. Any host system using more than 30 GB of storage is a candidate for SAN and NAS solutions and migration away from internal dedicated storage.
What is NAS?
Network Attached Storage (NAS) generally refers to storage and data that can be accessed directly from the network. With NAS, hosts or client systems can access (read and write) data and storage via a network interface (Ethernet, FDDI, ATM, etc.) using protocols including NFS and CIFS. NAS can be implemented using file servers, host systems running NAS software (NFS or CIFS), or thin servers called appliances. Some reasons for using NAS include:
- Storage sharing between multiple host systems
- Data sharing between multiple hosts and operating systems
- Overcome distance limitations using networking techniques
- Simpler management by reducing duplicate data and storage
- Application based storage access at file level
Traditional systems have either internal or external storage that is attached directly to a system, or perhaps shared storage as in the case of a large enterprise arrays. While external shared storage is an improvement over direct attached, there still exists performance and distance limitations with older SCSI and ESCON interfaces. Furthermore, even though storage can be shared, data cannot be shared unless special host-based sharing software is implemented. The most commonly used NAS software or application is NFS (Network File System) and CIFS (Windows shares) on NT systems. NFS is very popular and is standard on many systems with versions being available for most every system that supports a network connection.
What is a SAN?
Storage Area Networks (SAN) is a term generally associated with Fibre Channel today and can mean different things to different people. To some a SAN is anything that includes a Fibre Channel switch. To others, a SAN is only a SAN if it is used for backup. Others see a SAN as anything with two or more host systems using Fibre Channel. Rather than contribute to the debate of what a SAN is or is not, lets concentrate on using SAN to solve business issues.
- Reasons and benefits of using SAN include:
- Storage sharing between hosts
- High performance applications
- LAN-free backup
- Overcome distance issues
- Server and storage consolidation
Today, Fibre Channel SANs are being deployed using FC-AL (Fibre Channel Arbitrated Loop), also known as "private loop," and Switched or Fabric also known as "public loop." Both "topologies" enable systems to share storage using 100 MB/second interfaces with distances up to 10 km. SANs today are being used mainly for storage sharing and consolidation as well as for increasing performance and capacity for systems. SANs are beginning to be used for backup and other applications.
Complimentary or Competing?
Will SAN and NAS merge or converge? Yes. Vendors like MTI have been delivering integrated NAS and SAN solutions for some time now. Over time as groups like the SNIA ratify new enhancements and new specifications, the integration between SAN and NAS will become even better. A SAN can be utilized as a storage backbone providing basic storage services to host systems and to NAS servers. SANs today are well suited for storage sharing and building infrastructures for server and storage consolidation, as well as to address performance and capacity intensive applications. NAS should be used to solve data sharing issues and sharing of storage for small systems.
SAN should be used for storage sharing and high-performance, low-latency applications such as databases. A common mistake is to try to use SAN or NAS for everything rather than match the proper technology or for that matter, "access method" to the specific business and application issue.
Application or Scenario Access Method
Table 1: Application or Scenario Access Method | |
Storage or server consolidation | Use SAN |
Data sharing and movement between systems | Use NAS (SAN) |
Access by Unix, Linux, NT and legacy systems | Use NAS (SAN) |
Data sharing including Internet/Web content | Use NAS (SAN) |
Performance-sensitive with low latency (database) | Use SAN |
Large I/Os or data transfer applications | Use SAN |
LAN-free or serverless backup | Use SAN |
In the table above, (SAN) indicates that SAN storage sits "behind" the NAS server or appliance. This differs from host systems directly accessing SAN storage as block-level applications. While NAS provides data and file sharing using file-based access methods (NFS and CIFS) over standard network interfaces (Ethernet, Gigabit, etc.), SAN technology including Fibre Channel Switches, and Fibre Channel RAID arrays provide storage for the NAS server or appliance. Think of NAS as being an extra layer of intelligence that sits in front of the block storage being served by the SAN.
Summary
Whether SAN or NAS is better should not be the decision criteria for solving business issues, rather how SAN and NAS combined provide the best of both worlds. Take a look at your applications and business to see how SAN and NAS can collectively address various business issues. SAN and NAS implemented in a complementary solution help to reduce costs and simplify storage and data management.
About the Author: Greg Schulz is a Senior Technologist at MTI Technologies.