The Limitations of All-Flash Arrays

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    Flash is great, but it might not solve all of your problems: the pros and cons of All-Flash Arrays

    All-Flash Arrays are a popular solution to commercial storage expansion and updates. They are fast, small, energy efficient and increasingly affordable. However, are the right for you? 

    There are easy answers such as looking at if you need the speed boost Flash offers. It is equally important to consider the health of your existing infrastructure. The benefits of Flash are unlikely to outway the costs of replacing a state-of-the-art HDD system you just finished installing.

    There are, however, a number of other factors ranging from the type of applications you are running to the broader nature of your IT environment that you need to consider when looking at a Flash upgrade or investment. On a broad scale, it is almost always beneficial to think about hybrid solutions and build something tailored to your needs.  

    This article will walk you through these considerations and help you make the best choice for your organisation when it comes to All-Flash Arrays.  

    Is Flash Right For You?

    Things to consider when assessing the pros and cons of All-Flash Arrays

    The Limitations of All-Flash Arrays When Handling Code Written For Disk

    Code developed around the characteristics of the disk can cause unnecessary latency and system wear when running on Flash. Long code paths, the generation of significant metadata and the caching of large amounts of granular snapshots can become an issue for Flash drives.

    The primary cause of these problems is that Flash has to write information in blocks — meaning that in order to change one byte in a file, the entire block that contains that alteration must be rewritten.  This issue is called ‘write amplification’. If this is not accounted for, either in programming or write techniques, it can undermine some of the speed benefits of Flash and aggravate rewrite deterioration issues.   

    These problems can be substantially mitigated through compression algorithms, which many Flash systems use as a standard. A business can also sidestep this issue by rewriting their systems. More simply, the problem can be bulldozed through over-provisioning storage and memory capacity*. No matter how it is approached, this is something you need to consider before migrating to an All-Flash storage network.

    • Code written for disk can cause unnecessary latency and system ware
    • This can undermine the speed benefits sought after through a Flash upgrade
    • Compression, overprovisioning or re-writes must be considered to get the most out of Flash

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    The Limitations of All-Flash Arrays to Prioritise Information  

    Consider whether or not all of your data is equal. For many organisations, older data becomes ‘inactive’ — no one is interested in accessing it, but it can’t be deleted. Under those conditions, optimising access speed by purchasing an expensive new All-Flash Array is not particularly important.   

    The solution is a hybrid environment — something that can also be utilised to deal with the old code. The difficulties here are the IT challenges of migrating the right data to the Flash array and maintaining a multi-tiered system. Purchasing a storage accelerator can help solve this problem.

    • Consider the active value of all your data
    • Look at hybrid solutions to avoid investing in access high access speeds to data pools you never access
    • Think about how hybrid environments can improve performance when using AFAs and legacy coding in a segment of your organisation

    The Limitations of All-Flash Arrays: Are Hard Drives Actually Your Weak Link?

    You have to think about your overall network capabilities. If your connection speeds and network architecture won’t allow you to take advantage of the speed of Flash, you simply move your access bottleneck somewhere else. Buying an All-Flash Array won’t solve all your problems if your network is ageing or poorly put together. A Flash upgrade may need to be part of a larger network refurbishment to be really worthwhile

    • Flash won’t help you if limited by bottlenecks in other parts of your network

    Is Flash The Future Regardless of Its Limitations?

    The basics of what to look out for when it comes to hardware

    The short answer is yes — Flash Storage is the future. Despite its drawbacks, it is fast, small and effective. SSDs have historically been designed to accommodate HDD I/O interfaces — SAS or SATA. The future is hard to predict, but new advances in interfacing technology may change that and push All-Flash Arrays [AFAs] into a league of their own — particularly where enterprise storage is concerned.

    Nonvolatile Memory Express (NVMe) and NVMe over Fabrics (NVMe-oF) are already available and are interface protocols that allow for the access of memory through thousands of parallel command queues — rather than a traditional single series of commands. The speed capabilities these offers are truly huge compared to traditional Flash options and HDD capabilities.

    Storage-class Memory (SCM) or Persistent Memory (PMEM) is a developmental technology that operates as both memory and storage simultaneously or interchangeably. It is basically storage that is so fast that it can be used as a DRAM. This is something to look out for more than to think about purchasing today.

    • Flash is fast, small and effective
    • Flash is increasingly affordable
    • Advanced is Flash specific I/O interfaces are poised to push AFAs into a league of their own

    SUMMARY: Become Comfortable with Hybrids to Counteract the Limitations of Flash and All-Flash Arrays

    The efficacy of Flash generally comes down to time and budget. If you have the money and are operating without much legacy coding or hardware, Flash is a great choice. It is small, easy to use and fast.

    If you already have a lot of HDD capacity and operate in a legacy environment written for HDD, keeping much of that hardware around may be advisable and will certainly be economical.

    However, barring a quantum computing breakthrough — the future is Flash*. Because of the size and power efficiencies of Flash, businesses can save on rack space and energy costs, while achieving higher performance.  

    Hybrid solutions are definitely worth considering. There are a lot of options in the market, and you need to think about the hardware you already have and what you need to use it for.  Flash is truly optimised for an environment in which information is written only a few times and read many more — and where speed matters a lot. If this applies to you — Flash is your best bet*. If it only applies to part of your environment — think about ways to segregate your storage environment to get the best out of both worlds.

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    Although there is significant complexity accompanying data storage, most solutions offer flexibility with growth. There is an increasing number of hybrid control tools on the market, and it is less and less important to look at data storage as distinct choices — but, rather as a continual journey of optimising a number of different solutions. Flash is likely part of that journey and solution.  


    * How to overcome flash-based storage limitations to ensure efficiency
    * All-Flash Arrays Bring Big Benefits to Enterprise Storage
    * All-Flash Arrays: Benefits and Disadvantages

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    Troy Platts

    Troy has spent over 20 years helping organisations solve their data, storage and compute conundrums. He is a regular speaker at vendor events and spends any free time he has keeping abreast of advances in data platform technologies. He also makes a mean curry.

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