Advancing the State of the Art in PCIe SSD

Solid State Drives (SSDs) that leverage the PCIe bus provide the ultimate storage I/O performance boost by providing the CPU with direct access to zero-latency storage. But all PCIe SSDs are not created equal. There is room for advancing the state of the art so that the fastest storage can become faster, more reliable and more usable.

The OCZ Z-Drive Revision 4 (R4) is a bootable, PCIe Gen 2 x8 form-factor SSD storage solution, designed for application acceleration in enterprise environments. Available in two models, the half-height, half-length RM84 comes with 300GB to 1.2TB of usable MLC NAND flash capacity and the full-height, 3/4 length RM88 is equipped with 800GB to 3.2TB of usable capacity. Both versions of the Z-Drive R4 use multiple SandForce NAND controllers, four in the half-height and eight in the full-height. These advanced technology controllers run the flash translation layer (instead of running it on the host), reducing the impact that flash overhead tasks have on sustained performance.

A Very Fast PCIe Flash Solution

The Z-Drive R4 uses OCZ’s proprietary SuperScale* storage accelerator (direct memory access core) to enable 2.8GB/s of sequential throughput and 410K random IOPS performance for the FH RM88 model and 2GB/s of sequential throughput and 250K random IOPS performance for the HH RM84 model, providing industry-leading specifications. This performance, combined with OCZ’s Virtual Controller Architecture (VCA) 2.0, makes the Z-Drive R4 an ideal solution for virtual server environments where horsepower and flexibility are key requirements. The Z-Drive R4 supports Windows, Linux and VMware operating systems and is a bootable PCIe solution.

The OCZ SuperScale storage accelerator provides on-board processing resources which handle some of the protocol and data management overhead that would otherwise consume host CPU cycles. This improves application performance and helps to maintain that performance as workloads fluctuate. Each SuperScale controller can be represented as one or more LUNs using OCZ’s VCA, which in turn, allows direct access to applications or VMs, greatly increasing storage efficiency and design flexibility.

Virtual Controller Architecture

OCZ’s VCA is a virtualization software layer that creates logical storage pools which can be individually accessed by file systems, storage software, applications or VMs. This allows the flash capacity to be divided among multiple logical users or aggregated for a single user by establishing access paths into multiple LUNs.

Using an intelligent command queuing structure, based on OCZ’s proprietary Queue Balancing Algorithm (QBA), VCA balances drive loading and maximizes internal bandwidth to offer a nearly linear increase in performance as more LUNs are engaged. By allowing users to configure the performance resources to fit the workload, VCA provides maximum benefits to storage architects.

Flash Endurance

The process of consolidating pages and erasing data blocks is called “background garbage collection”, a process which consumes controller cycles. The copying of valid pages (causing “write amplification”) also adds to SSD controller overhead but can impact the endurance of the flash device as well, since NAND cells can only sustain a finite number of write and erase cycles. The VCA software layer supports the TRIM Command which allows the OS to communicate invalid pages to the SSD, enabling idle-time garbage collection and moderating write amplification.

The Z-Drive R4 architecture also provides a global wear leveling function. This enables a wider distribution of writes, spread evenly across flash cells, than is possible with other multi-controller devices. That capability improves flash endurance and lowers overhead on the flash controller, helping to sustain performance under increasing workloads. VCA also supports SMART to improve system administration of the SSD implementation. Based on past and present use analysis received from the SSD controller (via VCA) it provides advanced monitoring, reporting and analysis, and will start warning messages about potential drive failures.

Data Integrity

NAND flash is a persistent storage medium, meaning its data is protected in the event of a power failure. However, write cycles that are in process are still vulnerable, especially the metadata, which records where data blocks are written. OCZ’s DataWrite Assurance* technology provides a mechanism to protect this transient data. When a power loss is detected (the power source drops below a predefined threshold), the SSD controller stops accepting writes or any new commands from the host, until the in-flight write operation completes. Once this occurs, the SSD controller activates power loss backup circuitry to power the volatile memory as essential metadata is copied into flash.

Flash Cache

To complement Z-Drive R4 in virtualized environments, OCZ’s VXL cache and virtualization software provides intelligent flash caching of data into virtualized server platforms. This combined virtualization solution distributes flash caching resources on-demand across Virtual Machines (VMs) in that host, and in other hosts within the virtualized cluster. In addition, it distributes the flash between VMs based on need making sure that no VM inefficiently occupies flash when it can be better used elsewhere. It does this without impacting primary storage functions of the hypervisor layer, such as vMotion, Fault Tolerance (FT) and High Availability (HA). With its ‘SAN-less Data Center’ mode, VXL can provide a high speed, networked resource for improving application performance, resulting in better ROI as more VMs can share the benefits of this PCIe-based flash cache.

Storage Swiss Take

The focus for SSD vendors has historically been on performance. But as the technology matures users’ expectations start to include things like ease of implementation and ROI. These users assume flash devices can help solve an application performance problem, but want assurance that they can be up and running with a reasonable amount of effort and can keep pace with the dynamic environments they’re being put into. Users want a performance enhancement solution, not a bunch of SSD ‘parts’.

The Z-Drive R4 PCIe SSD series was designed for this requirement. In addition to its industry leading performance, it has a virtualization layer that simplifies implementation and provides the flexibility storage architects need to fully use that horsepower. VCA 2.0 supports the VXL caching software which allows multiple VMs to share resources on a single PCIe card and enables the use of MLC flash technology while supporting the flash management processes that extend device life and further enhance ROI.

* SuperScale and DataWrite Assurance are trademarks of OCZ Technology Group

OCZ is a client of Storage Switzerland


Eric is an Analyst with Storage Switzerland and has over 25 years experience in high-technology industries. He’s held technical, management and marketing positions in the computer storage, instrumentation, digital imaging and test equipment fields. He has spent the past 15 years in the data storage field, with storage hardware manufacturers and as a national storage integrator, designing and implementing open systems storage solutions for companies in the Western United States.  Eric earned degrees in electrical/computer engineering from the University of Colorado and marketing from California State University, Humboldt.  He and his wife live in Colorado and have twins in college.

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Posted in Product Analysis

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