Redundancy in enterprise storage networks using dual-domain SAS configurations technology brief Abstract.............................. 2 Introduction............................2 Why dual-domain SAS is important ....................... 2 Single SAS domain .......................... 3 Dual-domain SAS..........................4 Examples of redundant architectures using serial storage................5 Dual-domain SAS..........................5 Dual-domain SAS: servers in two-node cluster..................
Abstract This technology brief explores the issue of single points of failure within storage networks and how pathway redundancy addresses this problem. Appendix B of this brief explains the technologies that enable redundant storage networks and why the implementation is dependent upon serial drive technology.
archival, reference, and redundant highly-available applications. They are intended for use in an environment where the drive workload is 40 percent or less. Single SAS domain There are many single points of failure in a single domain. Failure can originate from any controller, expander device, JBOD or cable, as shown in Figure 1.
Dual-domain SAS Using dual-ported drives and dual controllers, or a controller capable of supporting dual domains, provides dual-path redundancy from the server. Figure 2 shows an example of a single controller capable of dual-domain support. The dual-domain SAS configuration in Figure 2 can tolerate simultaneous single port failure in a dual-port, dual-domain capable controller, external cable failure, and expander failure.
Examples of redundant architectures using serial storage This section illustrates some of the redundant storage scenarios made possible by serial storage, Smart Array, and cluster computing technologies. Dual-domain SAS This dual-domain SAS architecture provides redundant pathways for cascaded JBODs. Using two IO modules for each enclosure and SAS dual-port drives, this configuration provides redundancy throughout the storage network and eliminates any single point of failure.
Dual-domain SAS: servers in two-node cluster This configuration, which is also known as a high availability (HA) cluster, at least one server must have access to the storage network. The cluster interconnect provides redundancy in the event of host bus adapter (HBA) or cable failure, as shown in Figure 4. Dual-domain SAS requires “active/active” configurations.
HP dual-path with cascaded JBODs The dual-path approach can prevent a single point of failure occurring in complex enterprise configurations such as cascaded JBODS. The configuration is supported for both SAS and SATA drives. In this configuration a controller is connected to the IO module at each end of a set of cascaded JBODS.
Summary HP introduced dual port SAS hard drives during the last half of 2007. HP is now introducing products that support SAS dual port operation. As of this writing, the Smart Array P800 controller is capable of supporting two domains. The HP StorageWorks Dual Domain I/O Module Option Kit enables the 60 Modular Smart Array and 70 Modular Smart Array to support redundant pathways from servers to storage devices.
Appendix A: Nomenclature and definitions New technologies generate new descriptions and nomenclature surrounding those technologies. This section provides definitions for related concepts, technologies, and infrastructure terms related to storage network redundancy and dual-domain SAS configurations. Dual-path Dual, redundant paths between initiator and target ports can be in the same or different SCSI domains.
phy is a generic electronics term referring to an electronic integrated circuit or a functional block of a circuit that encodes and decodes transmissions between a pure digital domain (on-off) and a modulation in the analog domain. A ‘SAS phy’ is a combination of the physical layer, phy layer and link layer functions.
Appendix B: Enabling technology The advent of SAS and SATA drives makes the implementation of dual-domain SAS technology possible. Hardware and protocol commonality enables the redundancy and reliability of dual-domain SAS technology and reduces the number of possible single points of failure within a system. SAS and SATA technology Parallel storage technology has reached hard limitations with respect to volume and speed.
Connectors SATA drives are compatible with SAS connectors, but SATA connectors will not accept SAS drives (Figure B-2). Preventing SAS drives from connecting to a SATA network is important because SATA drives are, without the intervention of port selectors, single-ported and cannot accommodate the dual- ported pathways used by SAS drives.
Backplane The same keyed connection layout is applied to system backplanes allowing them to accept both SAS and SATA drives (Figure B-3). Figure B-3 Common backplane for Serial drives System Backplane One backplane accommodates both SAS and SATA drives… SAS Drives SATA Drives Devices The following devices make up dual-domain SAS networks.
A computing cluster must have a dedicated cluster interconnect to which all cluster members are connected. This interconnect serves as a private communication channel between cluster members and HP Smart Array controllers directing data traffic on existing domains The cluster interconnect is normally used for five high-level functions: •...
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