Modular vs. Monolithic

Modular's price is attractive and features have steadily grown, but modular still has advantages for some scenarios.

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Life is full of choices. Should you, for example, buy a big-box storage system from a single vendor or mix and match open system components? Remember, however, as your first-grade teacher annoyingly preached: "With every choice, there's a consequence."

And any choice offers pros and cons on each side of the issue. Monolithic and modular storage both take advantage of the movement toward network storage through consolidation, scalability, performance, availability and a better return on investment.

Comparison of modular & monolithic

There are strong benefits for each design - the hard part is choosing.
and reliability
Implementations should have path failover/redundancy in host I/O path, switch and storage components (dual drive bus, dual controllers, fans, power supplies, and hot spare drive(s) for immediate RAID rebuild process in the event of any disk failure). Remote mirroring and snapshot/backup techniques are available. Validates cluster server testing. Robust failover and availability. Initially led and still perceived to provide the premier remote mirroring solutions, although this gap is rapidly closing.
Connectivity SCSI, FC and iSCSI attach, however, lacking mainframe attach. Variations between vendors for number of logical volumes, channels and operating systems. ESCON, FICON, SCSI, FC connections for mainframe and open systems attach. Large server connectivity, but being matched by some modular.
Interoperability Getting much better, but not ubiquitous. Look for interoperability processes/certifications and standards (i.e., FCIA SANmark certification). Complete solutions available from various vendors. Some modular vendors lead the market in this area. Since these systems have the largest base, in general, more interoperability testing is available for their systems. As volumes shift towards modular systems, this advantage will go away.
Manageability Vendor-specific usability and capability. Check for dynamic, online scaling capabilities (i.e., adding disks, expanding volumes, changing RAID or configurations). Heterogeneous management products coming onto the market. Some vendors providing all management from within a single application. Probably requires service call to expand storage and change configurations. May have an advantage to stay with homogenous brand of storage. Each vendor has future strategy to manage heterogeneous storage. Often requires multiple applications to manage in open systems.
Performance For open systems environments, the Storage Performance Council has established the first industry standard benchmark for measuring I/O transactions per second, and modular storage came out a leader in actual performance and, scalable back-end channels and effective read-ahead algorithms assist in anticipatory reads in the random nature of open systems. Cache-centric architectures were developed to counteract the architectural limitations of the mainframe environments. The cache architecture - beneficial for mainframe performance - can't keep pace with the modular open-systems design which can scale controllers and back-end channels to the disks.
Scales controller modules and drive modules independently. Pay as you grow approach. Designed for simple expansion. Industry standard rack-mount cabinets allow flexible appliance integration. Vendor unique capacity per each storage system with some approaching same capacity as monolithic. Can attach storage to mainframe and open systems, but not recommended to have both on the same subsystem. Typically requires service call to add or partition storage. May accommodate more storage with fewer subsystems.
Service Vendor, channel partner dependent. Professional services not required. Ease of use can be built into software interface. Complete service and professional services offered and typically required. This can be valuable, but costly.
TCO Architectures, innovation and competition allow for much better pricing and scalability. Gartner estimates 25% savings on storage costs. Additional service and maintenance savings. Higher costs for open system-attach (Windows, Unix) and less performance, however, management of homogenous storage may be of value.

But, here's where it gets interesting: According to analysts, monolithic systems generally provide more robust failover, availability, interoperability testing and professional service. On the other hand, the little guys excel in scalability, performance, management and cost less.

Monolithic boxes usually come with the RAID controllers and disk drives in large, self-contained, one-size-fits-all enclosures. The majority of today's storage area network (SAN)-based storage is in large enterprises where mainframe class external RAID systems were established with EMC's Symmetrix and IBM/StorageTek's monolithic storage systems. Currently EMC's Symmetrix, IBM's Enterprise Storage Server (Shark), StorageTek's SVA, and Hitachi Data Systems' Lightning Series provide this large form-factor storage system capable of attaching to mainframes, as well as open systems server environments.

What's best for your environment?

Since each user environment is unique, below are some key areas to evaluate when selecting new storage systems:

Identify your current infrastructure and future storage needs.

Ensure your server systems are certified to work with the storage system.

Compare total cost of ownership including purchase, installation, service and manageability aspects.

Investigate premium features of your desired storage solution, specifically remote mirroring, snapshot and management software.

Compare scalability factors, such as maximum capacity per storage system, number of logical volumes, dynamic volume expansion, capacity expansion and configurations change options.

Consider the service and support. Compare the anticipated response time for new application deployments or configuration changes.

Finally, compare performance of the storage system in meeting your needs for large file transfers and/or transaction based I/Os per second.

In contrast, modular external RAID controller-based storage systems are defined by the distinct separation of the RAID controller module(s) from the disk drive module(s). Each module is housed in industry standard racks - which may also hold other general-purposeappliance servers - and separate the scalability of performance and capacity. Modular storage systems are targeted specifically at open systems servers, and typically don't carry the large cache and myriad of connections, Enterprise Systems Connection (ESCON) and Fiber Connectivity (FICON), which are required for mainframe storage. Examples of modular storage includes Compaq's EVA, EMC's Clariion, Dell's PowerVault, HP's VA7000 series, IBM's FAStT series, LSI Logic's E-Series, StorageTek's D-Series, XIOtech's Magnitude, and others. The analysts at Gartner, Inc. in Stamford, CT, are projecting that modular storage systems will exceed the revenue of monolithic storage systems in 2003, with a continuing growth trend favoring modular.

Benefits of modular storage

Modular storage developed in much the same vein as stereo components did: to satisfy a customer's desire for lower-cost gear and prevent vendor lock-in. For example, with modular components an iSCSI router can easily attach to lower-end servers that don't require the performance of Fibre Channel (FC).

A summary of modular storage strengths

  • Cost. Gartner estimates 25% less than monolithic. The actual cost comparisons can vary drastically and must be evaluated for each configuration.
  • Performance. Applications such as transactional databases, data warehousing, customer support ande-commerce place different, more complex demands on storage system performance than previous generation applications. Coupled with higher performing server technology, modular storage leads performance by supplying multiple back-end drive channels and sophisticated controllers with special read-ahead algorithms.
  • Scalability and flexibility. Systems can dynamically scale capacity and performance independently. Systems can start small and grow cost effectively.
  • Footprint. The latest disk drives and packaging allow for optimum capacity per square foot.
  • Manageability and usability. User-friendly interfaces and management tools have been designed to allow administrators to expand capacity, create new volumes, map new servers and other tasks that often require service calls in the monolithic storage systems.

Benefits of monolithic storage

The IBM 3XX mainframe systems of the late 70s and early 80s were limited in their performance due to the availability and cost of memory technologies. Mainframe storage vendors - initially EMC and IBM/StorageTek - developed cache-focused storage systems to counteract the architectural limitations of the mainframe environments. In the mainframe environment, it proved to be more cost and performance effective to place significant cache in the storage system relative to the mainframe to accommodate its more predictable, read-oriented applications. These large cache storage systems provided significant performance advantages in the mainframe environment.

Typically one or more storage systems were connected to each mainframe system. Initially, midrange servers - running Unix, NT and NetWare - each had their separate physical storage, either internally or externally attached. Eventually these large external RAID storage systems expanded from mainframe to also attach to open systems servers using a networked storage model. The advent of consolidated, networked storage provided the ability to logically divide storage, allowing for much higher capacity utilization.

The monolithic storage systems now offered with EMC's Symmetrix, IBM's Shark, StorageTek's SVA and Hitachi's Lightning series provide the following:

  • Connection. Both mainframe and open systems servers can be attached, although it's not recommended to use both on the same physical system.
  • Homogenous environment. With the large installed base of these systems, it may be advantageous to keep one brand of storage system.
  • Capacity in a single storage subsystem is greater than most modular storage systems.
  • Robust replication and disaster recovery. The largest installed base of replication products are on these systems which are perceived to have the most robust mirroring solutions, although this gap is closing quickly.
  • ISV integration. Many integrators are familiar with these established systems.
  • Service and support. Extensive professional services and support teams are in place.

The choice is yours

The good news is that storage technology is accelerating at a tremendous pace, bringing increased functionality and benefits. Most importantly there's more choice: There isn't a one-size-fits-all solution. Monolithic systems provide external RAID storage for mainframes and also attach to open systems servers. Modular storage systems have been designed to attach to open systems environments and provide a flexible, lower-cost alternative in these environments. As noted earlier, there are benefits to each design.

Monolithic storage systems are the only alternative for mainframe attach and may be viable for open systems servers, primarily if keeping with a single brand of storage. The additional cost of these large systems may be justified because monolithic systems provide a homogenous storage environment. They offer the most proven disaster recovery and replication products and usually come with the highest levels of service and support.

Modular systems, on the other hand, are more flexible and scalable and allow a pay-as-you-grow price structure. The management interfaces are often designed for end users, and as a result it's easier to expand capacity, manage volumes, provision storage and a variety of other tasks that would likely require a service call in the monolithic world. Performance is also superior in the open systems environments, and modular systems cost significantly less than monolithic systems. In addition, today most storage innovations first appear in modular systems.

The choices that are available offer increasing value to the customer and - with a little investigation - administrators can meet their storage needs today and have an infrastructure that accommodates their future requirements.

This was first published in September 2002

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