Historically, NAS and Storage Area Networks (SANs) have dominated mass storage needs in military, enterprise, and industrial applications. However, the global storage paradigm typically conjures up images of an external chassis interconnected via a Fibre Channel or SCSI interface. Traditional SANs and NAS require space for added hardware and cabling needs, often proving cumbersome or unworkable in harsh military environments.
By contrast, the relatively small footprint of 6U NAS blades enables use inside the box across many different applications where space constraints precluded older NAS configurations from consideration. In addition, conduction-cooled NAS blades now bring smaller footprints into avionics, where limited airflow for cooling is available.
With the introduction of new, integrated 6U products, NAS is gaining acceptance in military embedded computing as a cost-effective and reliable shared storage solution. 6U VME and CompactPCI versions now bring multiple drives, RAID controllers, improved processor speeds, and dual GbE links together for network bandwidths of up to 50 MBps for reads. Half TB capacities in a single slot using 2.5" rotating drives and up to 128 GB in 2.5" solid-state flash drives with Serial Advanced Technology Attachment (SATA) and Parallel Advanced Technology Attachment (PATA) technology are now achievable.
In accordance with these factors, blade-level NAS is stepping into the forefront, offering the high reliability and high availability required in modern military applications. Meanwhile, within the NAS family, solid-state drives are proving themselves a viable contender against more traditional rotating drives.
6U NAS with RAID provides additional reliability
The inside-the-box, high-speed, high-capacity design of NAS lends itself to a new level of rugged applications demanding high reliability and redundant operation. NAS with RAID is showing up in critical data repositories aboard ship, land, and air platforms that need protection against catastrophic events. Streaming audio and video applications in military settings dealing with increasing needs of storage data benefit from both smaller footprint systems and lower solid-state flash drive costs.
Blade-level NAS incorporating RAID can address the storage needs of harsh environment, mission-critical applications in scalable dual star systems (see sidebar). The NAS blade provides the necessary internal processor, network interface, RAID controller, and disk storage in a single-slot VME or CompactPCI form factor. At the blade level, NAS operates as a client/server model, using familiar protocols including NFS 3.0 and Common Internet File System (CIFS).
NAS blades can either be single slot with two drives or dual slot with four drives. Network complexity ranges from single star/single NAS blade with intra-blade RAID 0 or RAID 1 to dual star/dual-slot NAS blades with RAID 0+1, 1+1, or 5+1 and cross-network redundancy. Depending on user-specified configuration, such a system could supply two to four copies of the data.
However, reliability in harsh environments requires proper physical implementation. By incorporating pluggable drives into the thermal conduction frame, a solid-state drive-based NAS solution can be accomplished. An example of a conduction-cooled VME RAIDStor blade-level NAS is shown in Figure 1. It includes a VME PowerPC engine that can interface with two SATA drives to form a conduction-cooled NAS blade. The PowerPC processor provides high-throughput network performance, on the order of 80 MBps, while providing enough computing capacity to effectively run the file system protocols and the RAID algorithms. NAS network reads can be supported from 25 MBps in RAID 1 to 50 MBps in RAID 0.
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Equally important to reliability is user interface support for NAS management configuration, event detection, and administrator notification such as SNMP, Web browser, or Telnet. Blade- and drive-level hot swap helps avoid system power-down when replacing failed components. In non-cPSB systems, front-panel or optional rear-panel ports can be used for traditional cabled links. Through proper storage selection and redundant hardware duplication, as high as 4-nines system availability can be reached.
Extreme conditions require rugged considerations
New conduction- and convection-cooled blade-level NAS products with solid-state flash drives enable use in environments with shock and vibration requirements exceeding 10 gs at 11 milliseconds and temperature extremes reaching -40 °C to +85 °C where the more environmentally sensitive rotating hard drives experience higher failure rates. (See Table 1 for a comparison of currently available solid-state drives and rotating hard drives.) As recent flash drive cost declines have shifted users away from traditional rotating hard drives (for example, hard disk or floppy disk drives), rugged solid-state drives in combination with backplane embedded Ethernet standards and new 6U products are moving NAS into new applications and resolving issues of space constraints. Military and aerospace environments that have limited storage areas and contend with extreme temperature ranges are prime beneficiaries.
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Temperature extremes outside the typical 0 ¬∞C to +50 ¬∞C operating range for rotating hard drives predicate the use of solid-state drives in conduction- and some convection-cooled systems, because even the most advanced cooling schemes can’t reduce temperatures enough to extend rotating drive life expectancy. Recent solid-state drive costs have dropped by almost 80 percent, so rotating drives in many harsh environments might be nearing the end of their cost effectiveness, considering reasonable cost assumptions.
Industrial solid-state drives routinely operate at -40 °C to +85 °C with shock and vibration resistance exceeding MIL-STD 810F testing methods requirements (shock survivability levels at <10 gs at 11 msecs). Solid-state drive endurance is impressive with up to 10-year data retention capabilities and MTBF rates as high as 4M hours, with little or no downside operating in extended temperatures.
Conversely, rotating drive systems typically require expensive shock isolation and temperature management. Lower MTBFs trigger higher spares and maintenance costs, and rotating drives are rated at 500k hours for 0 °C to +50 °C operation, then derated in higher temperatures.
System failover versus high availability
In addition to high reliability in harsh environments, high availability in case of system failure is also critical in modern military applications. To cement a highly available storage design, engineers should consider the following:
- Data replication over multiple drives to cover drive failure
- Controller and interface replication to cover controller failure
- Data duplication between storage blades to cover blade failure
- Network path replication to cover network interface failure
- Data access by the application program
Implementing high-availability NAS blades requires features that address these functional issues. These include multiple disks organized as a RAID set within the blade, transparent duplication of user data between blades, redundant network paths and switching elements, as well as automatic failover between redundant NAS blades. Component failover times are key and must occur quickly and seamlessly without operator intervention, in order to improve system availability as the value of shared data increases with the number of host connections.
Designers are taking advantage of NAS benefits
Compact and rugged blade-level Network Attached Storage options now available allow embedded systems designers the opportunity to leverage the benefits of shared storage in applications where previous solutions could not have been considered due to space and environmental constraints. Price declines in form, fit, and function of solid-state flash drive replacements for rotating hard drives are beginning to erode economic barriers to flash drive utilization.
ACT/Technico
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