NextIO vSTOR Solid State Drive appliance

PCIe virtualization provides unmatched price-performance

By James E. Bagley
Senior Analyst, Storage Strategies NOW
May 2010

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irtualization of input-output makes it possible to share the latest generation of PCIe-based solid state drives (SSDs) between servers via dynamic reallocation of the I/O resources. NextIO has developed a bus-switching technology that provides a new level of flexibility for I/O device reconfiguration within a rack or adjacent racks. The advent of PCIe-based solid state drives from several manufacturers gives NextIO the ability to take advantage of the competition in this area and provides a unique value proposition for sharing these relatively expensive devices  (on a price per GB) across a server pool. The result is an extremely high performing storage array at a price-performance level that is only going to improve over time as new PCIe products enter the market and take advantage of new SSD advances.

Advantages of bus-attached SSD over drive emulation devices
The PCIe bus has a throughput advantage of nearly an order of magnitude when compared with a storage array accessed by a host bus adapter (HBA). A single x8 PCIe link provides 20Gb/sec of bandwidth.  With multiple server connections available there is plenty of aggregate bandwidth available for these devices as a pool of I/O resources. Since the work of managing the SSDs is accomplished in the drivers that run on the servers, the price per GB is excellent when compared with other enterprise SSD solutions, but the cost per Input-Output per second (IOPs), when compared with hard drive solutions, is really impressive. The practice of getting the highest speed storage closest to the processor is another well-known implementation, but without the ability to share resources, adding PCIe SSD to each server becomes an expensive proposition and increases the worry about a single point of failure. This leads to expensive over-provisioning of both servers and SSDs. The NextIO architecture, which provides a method of high speed switching of the SSDs between processors, solves this concern.

vSTOR models
The NextIO vSTOR appliance comes in two models, both based on the same I/O virtualization architecture, but differing in the type of memory, cost per GB and recommended use cases. Both vSTOR S100 models have 14 PCIe slots and can support up to eleven PCIe SSD cards and  up to five PCIe x8 lane server connections at 20Gb/sec bandwidth. This configuration flexibility allows significant customer choice in configuring for capacity versus server connections. Both models use a 3U (5 ¼-inch) high rack-mount format, and 28 inches deep, maintaining compatibility with IBM’s System X. The vSTOR Extreme uses higher cost but better write performance single level cell (SLC) flash memory. The vSTOR Standard uses lower cost but higher density multi-level cell (MLC) FLASH memory. MLC stuffs two or more bits per cell, delivering a lower cost per GB, albeit at the expense of slower speed, and a few other MLC trade-offs. The following table summarizes the models.

vSTOR Extreme  vSTOR Standard

Product SKU	Capacity	Random Reads	Product SKU	Capacity	Random Reads
S100-E01	1 TB	340,000 IOPs	S100-S01	1 TB	190,000 IOPs
S100-E02	2 TB	680,000 IOPs	S100-S02	2 TB	380,000 IOPs
S100-E04	4 TB	1,700,000 IOPs	S100-S05	5 TB	1,200,000 IOPs
S100-E05	5 TB	1,300,000 IOPs	S100-S07	7 TB	950,000 IOPs

Applications that need this type of throughput
NextIO recommends the vSTOR Extreme for structured data applications including database, metadata, and online transaction processing (OLTP) — all applications that need high transaction rates, low latency, fast response and workloads including read and write mixes. The vSTOR Standard fits better with non-structured data that are read- intensive. These include virtual desktop implementation, file and web servers and content delivery – applications that need multiple TB of capacity. As the throughput of processors has outstripped performance of hard drives over the last decade, a huge bottleneck has been created. Server and desktop virtualization, OLTP, database access, media-intensive applications and Exchange/SQL servers all represent areas where I/ O bottlenecks occur.

Server virtualization can take advantage of the processor compute capability but becomes bound by the speed of the storage media very quickly. Media-rich applications are driving demand for storage speed, as well as OLTP and virtual desktop implementations. Many of these applications can reach a level of 40 IOPS per user.  Even the fastest 15,000RPM short-stroked drives top out at about 250 IOPs. Five users per drive becomes an expensive storage bottleneck, especially in enterprises trying to support thousands of simultaneous users. In order to achieve the IOPs necessary to support thousands of users, massive over-provisioning of HDD spindles has been the only way to support the number of users.

Total cost of ownership analysis
In the following analysis, the number of users creates requirements for 250,000 IOPs and a database capacity of 5TB. In order to achieve the IOPs requirement, a system using 1,000 hard disk drives is compared to the vSTOR models. In this example, either vSTOR model can be used to meet the IOPs requirement. In order to serve the IOPs, massive over-provisioning of the HDD configuration yielding both high costs in capital expense and operating expenses.  Energy cost per year assumes $0.11 per kilo-watt-hour (KWH) and 100% duty cycle.

Configuration	Capacity	Total IOPs	Capital Expense	Watts	Energy cost per year	Total Cost 3 years	Savings
1,000 HDDs	44 TB	250,000 IOPs	$420,000	16,000	$15,418	$466,253	0
vSTOR Extreme	5 TB	1,700,000 IOPs	$200,000	390	$376	$201,127	$265,126
vSTOR Standard	7 TB	1,300,000 IOPs	$189,000	390	$376	$190,127	$276,125

SSG-NOW Assessment
NextIO has applied its capabilities for I/O virtualization to create an SSD storage appliance that can be shared by up to five servers without the penalty of going through another processor. This has tremendous advantages in terms of rapid resource allocation, minimization of over-provisioning and increased reliability by eliminating single points of failure. As a provider of a means to share openly available certified PCIe products, vSTOR customers will not be locked into a single source of SSD products. With rapid advancements in the SSD foundry business, and new entrants in the PCIe SSD market, NextIO is in a position to provide newly qualified products to its existing customer base, as well as enjoy the effect of Moore’s law without investing in SSD fabrication or integration of PCIe components and drivers. vSTOR and I/O virtualization provide a winning combination in a wide variety of applications and use cases.

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