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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.
KEY STORAGE
ATTRIBUTES		 MODULAR MONOLITHIC

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Availability
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.
Scalability/
flexibility		 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.
 Gap closing or may have some area of benefit
 Advantageous position

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.

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.

This was first published in September 2002

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