Best Dell Storage: Fibre, iSCSI, or Direct Attached?

Posted by Ryan Brown on Jul 01, 2018

Technology within the world of enterprise class storage is evolving at a higher rate of speed than ever before.  Three different standards have emerged within the industry.  Each having its own set of advantages depending on the type of situation they are implemented into.  Dell’s new PowerVault MD36xx series of storage arrays are designed to bring you a variety of different connectivity standards while simplifying your storage topology.  iSCSI, Fibre Channel, and direct connected SAS arrays are all represented within this latest incarnation of Dell’s PowerVault storage line.

When choosing between the aforementioned set of connectivity standards, it helps to know what the differences truly are.  The most mature and implemented among the three is Fibre Channel or simply put FC.  Ratified in the mid 1990’s it has long been touted as the de-facto standard among enterprise level storage area networks.  With operational speeds ranging from 1GB up to 16GB its speed is based on the type of cabling used and the protocols used to transport the data in question.

FC does not utilize any Ethernet based protocols like TCP/IP and is much more efficient at moving larger packets of storage data across its networks.  On the down side it is very expensive to implement and maintain, requiring its own specialized switching and HBA’s.  It has some pretty significant distance limitations as well, only being able to transmit data at up to 100 meters.  Without experience personnel in place to manage your FC network it gets dangerous to your infrastructure to operate.

iSCSI came into existence in 2004 and has been growing in popularity in the small to medium enterprise market ever since.  Depending on who you talk to, you will hear that iSCSI operating over traditional Ethernet is comparable to the speed that FC but can have performance issues because of the shared line and overhead.  One does not need to have FC experienced SAN technicians on staff and your average network administrator can implement an iSCSI SAN without much trouble.

On the down side, iSCSI requires software level initiators to function.  Much of the packet processing also gets offloaded onto the systems processors.  The ease of deployment covered earlier can also be a potential pitfall as well.  It is very easy to get an iSCSI deployment wrong from the first step.  Not using dedicated iSCSI NIC’s, lack of support for jumbo frames and flow control, and errors in the configuration of multipath I/O can lead to severely degraded performance.  With an easier setup and potential similar speed, iSCSI should be included as an option when evaluating FC for most implementations.

Finally we have external SAS technology that has been on the rise over the last half a decade or so.  For entry level SAN need SAS provides a cost effective direct attached alternative to iSCSI and FC’s network attached arrays.  While SAS cabling cannot travel nearly as far as Ethernet or Fibre, it can operate at nearly the same speed.  From a theoretical standpoint, SAS’s port technology is far superior to FC and is evolving just as fast.

SAS does have its limitations as a standard though.  Being a direct attached connection, you are limited in the number of servers connected to a SAS array.  There is no real convergence between SAS and FC like there is between FC and Ethernet.  FCoE or Fibre Channel over Ethernet has made for some reasonable amount of interoperability between the battling standards.  There is no talk on the horizon of such convergence for SAS based storage.

With all three prevailing storage standards at your fingertips the Dell MD 36xx family of storage arrays provides the ultimate optimization of your data storage infrastructure.  Invest in whichever of the connectivity standards makes sense for your business and have the peace of mind that all Dell PowerVault users experience.

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