Seite 2: Interview zu VCA 2.0

OCZ war so freundlich uns ein Interview mit Alessandro Gilligan, einem Mitarbeiter der Entwicklungsabteilung, zu VCA 2.0 zu gewähren.

1. What to do if SATA III interface is not enough performance?

Intel already presented details of the new „Next Generation Form Factor“ (NGFF) in one of the technical sessions of the IDF. The standard is aiming on two things: first – increasing performance for SSDs significantly and second – making smaller notebooks (Ultrabooks) possible. According to Intel mSATA modules with 5 mm high are too thick, and the SATA protocol itself with 6 GBit/s is too slow. After nearly a decade, it’s time for a successor. SATA will become a pure marketing name. An increase in SATA performance is no option for Intel. Sending more than 8 GBit/s via a single lane, is a difficult challenge. But this would be necessary for other compatible devices and connectors. While ago the SATA consortium has announced that all existing cables are not reliably transferring 12 GBit/s. That becomes clear when developing SAS 3.0 (Serial Attached SCSI with 12 GBit/s). The cost for a new SATA version would increase significantly. Multilane SATA is not provided. Due to Intel this would be possible, but would make new connectors and cables needed. Instead operation with efforts, Intel will start new and taking the finished PCI Express for this tasks. With PCIe in the third generation 8 GBit/s are longly possible. NGFF modules should also be multi-lane capable. Therefore with PCIe 3.0 already 16 GBit/s would be possible if two lanes are used as x2 configuration. Although mSATA modules are used in mini-PCIe slots, they will not be faster than SATAs 6 GBit/s.

2. What is the difference between SATA, SAS and PCIe?

SATA stands for Serial Advanced Technology Attachment. Because SATA is limited to 32 outstanding requests and is less scalable than other interfaces, it is optimized for lighter workloads like those typically found on desktop PCs and embedded applications. Maximum SATA transfer speeds are currently 6Gb/s, and there are no plans for increased speeds. SATA devices can be used in SAS hosts, but SAS devices cannot be used with SATA hosts due to the configurations of pins and slots. SATA devices offer the best price per gigabyte for smaller workloads where maximum speed is not required.
SAS stands for Serial Attached SCSI and is the traditional interface for enterprise storage. It can handle up to 256 outstanding requests and is highly scalable. Because of broad industry support, the market for SAS SSDs benefits from strong investment by SSD manufacturers, including SanDisk. SAS SSDs are compatible with contemporary RAID architecture. For applications that demand high performance, SAS SSDs are a logical choice, offering support for 6Gb/s speeds today and a clear roadmap for 12Gb/s speeds and beyond.
PCIe stands for Peripheral Component Interconnect Express. As the name implies, PCIe was designed as an I/O interface between various peripheral components inside a system. Unlike SAS and SATA, the PCIe is designed to be an I/O expansion interface and not a storage interface; these cards require a driver to function, so they are not widely used as primary storage.
Of the three interface types, PCIe is the fastest and sit closest to the CPU, making them ideal for I/O intensive application acceleration or as a caching solution.

3. Why choosing a PCIe RevoDrive instead of two or 4 single SSD cards in RAID mode?

This depends on what you are expecting from the RAID. Do you want to increase availability or performance?
In RAID 1 your data will be written simultaneously to two or more drives. While reading performance will increase, the writing performance will drop significantly and you have only half of capacity. Example two 500GB drives in RAID1 will provide 500GB available capacity but with a high availability of data.
In RAID 0 your data will be written alternately in two (or more) drives to increase performance. Here you have the most capacity per Euro.
In general Intel’s driver package called Rapid Storage Technology (RST) in the current version is delivering ATA-TRIM capable drivers for both AHCI and the RAID mode of the SATA controller, but is only works with single SSDs and not with flash drives in RAID modus. So additionally to your effort in building the raid and buying the single components you also have disadvantages in using all SSD features
With the OCZ RevoDrive 3 Series you will get a complete solution which is bootable and made for just plug it in and it works.

4. Is TRIM possible in RAID mode? How can drive performance be restored in RAID mode?

TRIM is not supported in RAID mode at this time. OCZ SSDs feature built-in garbage collection to ensure optimal performance after time, and you can also create an image of your RAID array to be restored following a secure erase of each individual drive. Secure erasing each SSD and then recreating the array will allow for maximum performance.

5. What is VCA 2.0? What are the most interesting benefits of VCA?

Virtualized Controller Architecture™.
The follow up to the original VCA presents as a complete storage subsystem, but with an improved and expanded feature-set allowing system architects unprecedented flexibility and industry-leading performance and reliability. Consolidated SMART support provides system administrators with advanced features for monitoring analyzing and reporting device attribute, while user-selectable data recovery and non-stop modes allows for unprecedented data protection. Unlike other flash virtualization layers, OCZ VCA 2.0 supports complete power fail protection; OCZ enterprise PCIe devices store all metadata in nonvolatile memory while power fail protection completes all in-progress transactions in the event of an unexpected system power loss.

6. Which objectives were pursued in the development of VCA 2.0?

OCZ wanted to take enterprise storage to new performance heights while maintaining the complete scope of data management and maintenance features, in essence, a ‘virtual super controller.’ OCZ’s proprietary VCA 2.0 is the next step in the evolution in enterprise flash virtualization layers. Supporting a rich enterprise feature-set, VCA enables system architects unprecedented flexibility and industry-leading performance and reliability when designing the high throughput storage systems of the future.

7. How does it work?

VCA 2.0™ supports the creation of a virtual pool of logical units (LUNs) and features best-in-class configurable performance aggregation, and is the only virtualization layer in the industry with TRIM and SCSI Unmap Support to enhance sustained performance by significantly reducing the overhead associated with garbage collection.
VCA provides highly efficient performance aggregation across physical LUNs via an intelligent complex command queuing structure that utilizes both native and tagged command queuing (NCQ, TCQ). This is a unique technology that enables command switching and balancing based on OCZ’s proprietary Queue Balancing Algorithm (QBA™) algorithm; this balances drive loading while maximizing internal bandwidth for nearly linear performance aggregation. VCA 2.0 LUNs can be further aggregated through cascading with host-side striping dependant on the storage architects needs. VCA is able to address NAND flash in an innovative way through the use of a massively parallel array, eliminating bottlenecks by increasing both read and write speeds up to the theoretical interface limit while keeping access latencies to a minimum.

8. What makes the difference of RAID solutions with or without VCA? How can I implement VCA 2.0 on my storage system?

With VCA, IT Architects can now take advantage of enterprise-rich features that are not available when utilizing traditional RAID cards with an array of SSDs in their servers. Clients can now overcome this obstacle and deploy a single, streamlined solid state drive storage solution that not only delivers exceptional bandwidth but also beneficial enterprise features including TRIM, SMART monitoring, native command queuing (NCQ), tagged command queuing (TCQ), power fail management, and wear-leveling.
OCZ VCA 2.0 supports the industry standard SCSI command set over our PCIe interface. Because SCSI is the command set of choice of enterprise storage architects, this feature makes installation of OCZ PCIe devices in enterprise applications seamless. VCA technology can interpret and execute both SCSI and ATA commands across any physical interface and utilize any available internal interface to facilitate communication across multiple elements of the overall drive architecture. Current OCZ hardware implementations support SCSI commands over PCIe (Z-Drive) and Serial (Talos). This storage virtualization currently allows SCSI commands to be sent through PCIe or SAS physical interfaces to an internal virtualized array of NAND devices.

9. What drives have been deployed with VCA 2.0 technology?

OCZ Z-Drive R3 PCI-Express SSD was the first drive to implement this new technology, and VCA 2.0 is now available on OCZ's enterprise class and workstation class PCIe SSDs including Z-Drive R4 and the RevoDrive 3 Series. Coming soon will be the Vector PCIe drive which will puts the performance of the Vector drives behind OCZ’s VCA 2.0 technology.

10. What is the maximum size of a PCIe based VCA 2.0 supported drive?

The maximum amount that we’ve put behind our SuperScale controller is 4TB. VCA 2.0 can support upwards of 16TB.

11. What is the maximum theoretical bandwidth of a PCIe 2.0 card per lane?

Today's second-generation PCIe interfaces offer speeds up to 5GT/s (gigatransfers/second) with a roadmap to 8GT/s and beyond. As the PCIe becomes more popular for performance acceleration in servers and workstations, manufacturers are working to improve the PCIe interface to meet the storage and serviceability requirements for the enterprise.

12. Will there be any versions of the RevoDrive with more than four parallel controllers and memory chips in the future?

We definitely have further plans for PCIe. As you can see, we have the Vector PCIe coming out next quarter, so our focus will be on this for the time being for the client side. Our engineers are constantly working on the next big thing, so definitely keep your eyes open for some very interesting stuff within the next year or so.