10 Advantages of SAN vs. DAS

Thursday Feb 17th 2011 by Kenneth Hess

SAN has many advantages over DAS in your data center. Here are 10 reasons to consider making the leap from local storage to a SAN.

Thinking of reasons not to use a storage area network (SAN) will not make the technology go away. Your out-of-control storage needs aren't going away either. And, before you mention network attached storage (NAS), you know its performance doesn't meet your needs. Why not cut your losses, admit your mistake, leave local storage in the past, and head for the SAN dunes of the future? Your move to a SAN is inevitable. Here are 10 reasons why you should take the SAN plunge and enjoy your decision to do so.

1. Scalability

If you know, or have heard, one thing about a SAN, it's scalable. What does scalable mean? SAN scalability means that you don't have the limit of a handful of disks that you can attach to a system. SANs can grow to hundreds of disks in size, whereas your server has a physical limit of about a dozen.

2. Performance

SAN performance isn't affected by Ethernet traffic or local disk throughput bottlenecks. Data transmitted to and from a SAN is on its own private network partitioned off from user traffic, backup traffic and other SAN traffic.

3. Data Isolation

There's no chance of your data being copied or stolen by anyone sharing the same SAN with you. Not even the SAN admins can see your data. When correctly configured, SAN data is zoned. These zones protect your data from everyone else's on the same SAN. An example of SAN zone separation is how UNIX servers can connect to a SAN and Windows servers connect to the same SAN, but the data that each group of servers accesses is different. In effect, Windows systems can't "see" UNIX data and vice versa.

4. Uptime

There's nothing quite like a SAN to assure 100-percent storage availability. SAN systems require no reboots to add new disks, to replace disks or to configure RAID groups. The ability to stream data between SANs for data backup and recovery also increases performance by bypassing server systems completely.

5. Workload Isolation

Zoning also separates your workloads from one another on a SAN. Not only is your data protected by zoning, but it also provides a barrier against other non-related workloads from affecting your application's performance. Sharing a SAN isn't a performance problem for applications when zones are in place.

6. Long Distance Connectivity

SANs have the advantage over all other storage connectivity for distance at 10km (about 6 miles). Not that you'll necessarily use that distance capability, but it's there if you need it. Having the advantage of distance allows you to consolidate your storage into an isolated location dedicated to storage and separate from the systems it serves.

7. Increased Utilization

Rather than hundreds or thousands of partially utilized local disks wasting power and generating heat in your data center, you could have dozens of SAN disks have no wasted space on them. How so? Thin provisioning on the storage side (i.e., on the SAN) uses space more effectively than local storage does. As a system requires more storage, the SAN allocates it dynamically. Yes, this means that physical systems can enjoy thin provisioning just like your virtual ones do.

8. Bootable

Despite the benefit of more fully utilized disks, as highlighted in advantage No. 7, you do not need to use local disks for the server operating system. It's possible to run diskless physical servers and boot directly to the SAN for your operating system, swap space (pagefile), and all applications. That's right, just like virtual machines.

9. Centralized Management

If you have SAN arrays from several different vendors because your data center has grown over the years, stress not, SAN vendors have created software management tools to manage your heterogeneous environment with ease. But, better than multiple vendor management capability, all of your SAN environments can be centrally managed from this single interface. This capability provides efficient and centralized storage management.

10. Disaster Recovery

The cost of a SAN is high. As you can see, there's no entry for SAN being a particularly frugal technology in this list. However, in the case of disaster recovery, a SAN can and does earn back its high price by providing a speedy recovery when the clock is ticking. A SAN is a reliable and fast data recovery solution. Server systems might go offline, but the SAN remains available.

Ken Hess is a freelance writer who writes on a variety of open source topics including Linux, databases, and virtualization. He is also the coauthor of Practical Virtualization Solutions, which was published in October 2009. You may reach him through his web site at http://www.kenhess.com.

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