A systems administrator is building a direct-attach, high-availability storage solution that will be shared by two rack servers. Each server has its own 12 Gb/s SAS HBA, and the external JBOD enclosure routes two independent links from every drive bay-one link to each HBA. The design goal is for the disk set to remain online if an HBA, cable, or I/O module on either path fails, without using interposer boards or additional electronics. Which type of disk interface must the administrator order for the eight drive bays to satisfy these requirements?
Dual-port 12 Gb/s SAS drives
12 Gb/s SAS drives that use a single wide x4 port for bandwidth aggregation
NVMe U.2 solid-state drives over PCIe Gen3 x4
SATA III (6 Gb/s) drives attached through a port multiplier
Only dual-port SAS disks expose two completely independent target ports on the drive itself. In a dual-domain topology each port can be cabled to a different HBA, so the operating system or RAID controller can continue I/O through the surviving path if the other path fails. SATA drives are single-port devices; they would need an interposer or port-multiplier and still could not provide true redundant access. NVMe U.2 SSDs attach over PCIe rather than SAS and cannot connect to the mini-SAS HD backplane used in this design. A wide-port SAS implementation aggregates several PHYs for more bandwidth between controllers and expanders, but an individual drive still presents only one domain and therefore does not add path redundancy. Dual-port 12 Gb/s SAS drives are therefore the only option that meets every stated requirement.
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What does 'dual-port SAS' mean, and how does it enable redundancy?
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What is the difference between a single-port and dual-port SAS drive?
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Why can’t SATA or NVMe drives provide the same redundancy as dual-port SAS drives?