How to choose the best flash storage for your data center?

The all-flash data center is a futuristic concept, and there are also many ways to implement server or array-based flash storage in the data center.

You can replace any data center storage system with flash, but should you?

Flash storage devices in modern data centers range from fully flash or flash cache-based disk arrays to server flash and as part of hyper-converged systems, with a wide variety of derivative technologies.

All-flash storage companies such as Nimble Storage, Pure Storage and Violin Memory have all made a lot of noise about how their arrays can replace existing data center storage systems.

EMC, NetApp and Hitachi Data Systems are taking a completely different view in this hardware arena, including flash as part of the overall storage architecture, but not necessarily replacing it.

*** Flash storage options depend on expected use cases, price maximums and storage minimums in the data center, as well as building constraints and performance requirements.

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Flash storage array

In terms of raw storage capacity, traditional disks still win. Although SSD density is increasing, mass-produced products are still stuck at 1TB. Current mass-produced disks are up to 6TB. SSDs are also more expensive than disks. However, on flash-based arrays, intelligent data management can reduce the cost difference to a negligible level compared to data load.

Flash memory is inherently faster than disk. Instead of seeking to find data bits, flash memory systems work on silicon crystals. Without the delays required to find and read data, flash memory also has much higher IO than disk.

Some disk arrays compete with all-flash arrays by using a small layer of flash storage as a data cache. Intelligent data management techniques identify "hot" (frequently accessed) data and send it to flash, while cold data is kept on disk. If data management is poor, the array will experience slow response times because it needs to search flash and then disk to get information. In addition, if the main performance problem is data writing rather than reading, then adding a flash buffer layer is not a good idea.

The future of disks

Finally, there are new types of disks - those that store near-line data archives rather than active data. Disks are not going away in the near future. More underestimated storage vendors will continue to develop faster rotational seek disks, which have characteristics that make them suitable for more data centers.

Flash storage has a different lifespan than disks. Disks can fail because of the head, platter, motor or actuator, none of these issues exist on SSDs. Every time data is written to a flash system, it goes through a certain number of program/erase (P/E) cycles. Flash substrates are designed to take a certain number of P/E cycles, although manufacturers use various techniques, such as heuristics, to improve the lifespan of the entire array.

The main type of flash storage, multi-level cells, can fail. So enterprise-class SSDs have different multi-level cells (EMLC) that can enhance the life and function of flash. Single-level flash storage is faster, but has lower storage density than EMLC and is more expensive. Some manufacturers believe that SLC is higher than EMLC in potential storage tiers, but most flash arrays use EMLC to support the main load and use the main capabilities of flash to improve overall performance.

Server Flash

Instead of investing in flash storage arrays, data centers can also install flash on servers. Flash drives are connected to PCIe cards on the motherboard, which optimize the data rate to the CPU. This can improve the performance of a single server, but it is also difficult to achieve resource concentration. There is also an additional option, which is to use server-side flash virtualization, such as PernixData FVP.

The next level of storage is DIMM, which has faster interconnect capabilities. DIMM flash memory can be installed in the computer system, just like memory chips. The technology is persistent - data can reside in the DIMM even when the computer is not powered on.

Some flash-based storage array vendors say that storage tier management is not important for flash because the performance advantage over disk is so obvious. But this is not the norm. Systems with flash storage arrays and a mix of server PCIE flash storage and DIMM flash systems will require very careful tier management.

Editor's note: An operations blog from Violin Memory points out that all-flash data centers can gain new revenue sources, reduce operating costs, simplify operations and gain more potential benefits. Similarly, Pure Storage also proposed that all-flash data centers are a way to accelerate business and drive new initiatives. At the same time, EMC advocates flash pragmatism, and Hitachi is exploring how to more seamlessly integrate flash into existing storage technologies.