Jul 072008

Have you heard of the Frame vs. Frame-less SAN debate? In the 10 years that I’ve been designing and implementing Storage Area Networks (SANs), I never considered an alternative to the traditional frame architecture, until I discovered EqualLogic – a frame-less SAN architecture. First, some legacy SAN background.


Frame based SANs

Most of us are familiar with frame based SANs that are assembled much like lego sets starting with an empty “frame” (the physical manifestation may be a rack). These are the well known products from companies like EMC, Hitachi (HDS), Network Appliance (NetApp) et al. To build out a “frame based” SAN we first need to assemble the components as follows:

  • Head unit (1 or 2) 
  • 1 or 2 storage processors (SPs)
  • Cache
  • Network connections
  • OS software
  • Add-on software
  • Disks – varying capacities and performance characteristics

Frame Issue 1 – Over Provisioning
Since Frame-based SANs contain individual components that scale independently (you can add more cache, network connections, disks, software, etc.) they require a significant amount of effort to come up with an initial configuration that will satisfy current and future needs. Most administrators dread upgrading storage arrays because it generally means hours or even days of downtime so in many cases customers will over provision the initial storage unit. Instead of simply buying what is needed today, customers will overbuy cache, network connections and disk space wasting money. What’s worse is that bloated frame configurations often become technically obsolete long before the maximum capacity or performance is reached.

Frame-LESS Solution
The frame-less architecture is different. Each “bank” of hard drives, say 16, includes it’s own storage processors, cache and network connections. To add additional storage in the future, you simply buy another “brick” which includes a small set of all the components. The frame-less unit’s operating system has the intelligence to “glue” the 2 bricks together into a single, virtual group without taking your host servers offline. As new drive technology becomes available, you can easily procure a higher speed/capacity “brick” unit and simply soft-attach it to the original group.

Frame-LESS Benefit: Modular storage bricks that can be seamlessly glued together allow you to defer buying capacity until you need it.

Frame Issue 2 – Decreased Performance when Adding Capacity
Another issue with frame-based SANs is that over time most customers will add additional disk drives to an existing “head” unit decreasing the storage processor to drive ratio. Adding more drives to a unit that has a fixed amount of SPs, cache and network connections means that each drive gets less attention and the entire unit becomes slower. Often vendors pitch “100+” drives per unit not bothering to mention that performance across LUNs will be negatively affected be cause of the lack of head resources.

Frame-LESS Solution
A frame-less solution, on the other hand, forces you to add the appropriate amount of additional SPs, network connections and cache automatically. Adding 16 more drives? You’ll also be adding 2 GB of cache and (2-4) 1Gb Ethernet connections. For a 32 drive system you would now have 8 active 1Gb Ethernet connections and 4 GB of cache. That is smoking fast!

Furthermore, you are now load balancing all LUNs across 32 drives (minus spares of course) so performance actually increases when you add units. Most frame vendors will counter this argument by saying the frame-less architecture forces you to buy more components you already own but the truth is the frame-less architecture, even with all of its redundant components, will still be less expensive. See for yourself. Get a Self-Service Price for a 12TB system right now.

Frame-LESS Benefit: Eliminate scaling worries; the larger it gets, the faster it gets.

Frame Issue 3 – Hot Spots
As a frame-based SAN is implemented individual Logical Units, or LUNs, will be defined. Whether or not that LUN is used for file or block data depends on the application using it. If a SQL database is placed onto a specific LUN then only the disks in that LUN are used to service DB requests. Other disks in the same array that are in separate LUNs may not be used by the DB application. Let’s say the remainder of the disks are being used for storage of file type data like office documents; presentations, word documents, etc. Hot spots occur when one application, like the database, is used much more than others. The LUNs that contain the database will be used the most and those drives may see 100 times more activity, leading to premature drive failure. Ironically, hot spots are a known problem with frame based architectures and the applications that are used the most are the ones whose drives will theoretically fail the earliest.

Frame-LESS Solution
A frame-less architecture distributes all LUNs across all available drives so all drives are used equally. This not only improves performance because there are more drive spindles handling the workload, but it also evens out the duty cycle and lengthens the average Mean Time Before Failure (MTBF) of the drives. This drive load balancing is automatically enforced as each new “brick” unit is added (unless manually overridden).

Frame-LESS Benefit: Hot spots are eliminated by always striping LUNs across all available drives

Frame Issue 4 – Cost
Frame architectures have been around a long time (most since the late 1980’s) and most come with very complex pricing schemes. A typical SAN configuration may have dozens of hardware, software and service pieces that must be chosen (see an example of the madness). This complexity and confusion means money for the vendors.

Frame-LESS Solution
Simpler is cheaper. A frame-less solution generally only has one part number that includes all the drives, SPs, cache, network controllers and software. All software functionality is included and there are never any surprises that you didn’t buy what you need. Furthermore, with an all-inclusive pricing model any future functionality will be included at no charge.

Frame-LESS Benefit: Less complexity saves you money

Summary of Frame-LESS benefits:

  • Don’t over-provision and buy more than you need today; add seamlessly in the future with higher performing “bricks”
  • Performance increases as a frame-less unit grows; eliminate scaling worries
  • Forced drive balancing eliminates hot spots; critical apps run faster, longer
  • All-in-one pricing is simple and saves money

The Frame versus Frame-less debate has just begun. There are only a handful of frame-less solutions in the marketplace today with the leader being Dell/EqualLogic. If a potential customer is looking for a lower cost, less complex SAN solution, then a frame-less architecture deserves to be considered, even for Tier 1 data applications.

Considering a new project that requires enterprise class storage? Be careful not to get FRAMED!

 Posted by at 4:40 pm  Tagged with: