What is Flash Storage? | Solid-State Storage | Hitachi Vantara
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What is flash storage?

What is flash storage?

Flash storage is a form of solid state storage, which is persistent computer storage made up of flash memory. Flash memory, integral in many storage devices, like USB flash drives, SD cards, solid-state drives (SSD), is a non-volatile computer memory storage that uses circuits instead of the electromechanical spinning disks that are found in typical hard drives. Non-volatility means that flash storage is persistent, and data remains when power is shut off, unlike random-access memory (RAM), which erases when powered down. The two main advantages for flash memory is speed of memory access, and lack of moving parts (disk platters, actuator arms, etc.). These two qualities have made flash memory more expensive than other storage options, but also significantly more versatile since flash memory enables many smaller and more rugged computers and devices today.

In fact, flash storage within the enterprise cloud context is replacing spinning disk technology in many applications faster than anticipated, especially as costs for solid-state memory continue to reduce. To be sure, Amazon Web Services (AWS), Microsoft Azure and Google Cloud Platform (GCP) are investing heavily in solid-state storage as well, but the superscalers like Facebook and Google will continue to utilize spinning disks, they are simply cheaper at scale. The speed that flash storage enables will also become critical as these companies' pursue high performance object-based storage. Moreover, flash storage can help to enhance the performance of virtual machines, making it easier to migrate workflows from on-premise machines to the cloud.

There are two types of non-volatile memory used for flash memory, each with their own properties that make it suitable for particular use cases. The two forms are NOR and NAND flash. NOR memory is slower than NAND memory in writing and erasing, but allows for byte level random access, because of this reason, it’s suitable for ROM use cases. But NAND, being faster, and providing more dense storage capacity, are used in flash storage use cases, such as solid-state drives.

Pros and cons of flash storage

As technology improves there is more applicability for solid state storage and memory than mechanical alternatives, which have many small moving parts that are prone to damage. But solid state still has some drawbacks, first the advantages of using flash storage.

Advantages

  • Speed — Flash memory is by far faster compared to hard disk drives.
  • Durability — No moving parts mean that flash memory is suitable for mobile and high impact scenarios.
  • Reliability — No moving parts also means greater reliability than drives with moving parts.
  • Efficiency — Flash memory is faster, and requires less power to operate than the electromechanical drives.
  • Portability — Flash memory’s small footprint makes it highly portable. For form factors that need to be small, flash memory is a suitable option.

Disadvantages

  • Cost — Spinning plate drives are simply cheaper to manufacture than flash memory.
  • Lifetime — Flash memory degrades during use, and degrades faster than hard disk drives. While this may not be immediately apparent on the consumer end, enterprise data volumes will push flash storage lifetime capacity to its limits.
  • Capacity — Flash memory is troubled to reach capacities above 1 TB. This limit is particularly challenging for data centers.
  • Electronic Corruption — While flash memory is good for devices found in dynamic scenarios, thankfully for their durability, they still remain vulnerable to electronic corruption, which can render memory unreadable.

Types of flash storage devices

Many of the typical storage units have flash counterparts, where spinning disks are replaced with flash memory.

  • SSD Flash Storage — Found in many laptops, solid-state drives have been used to slim down device form factors, while reducing weight. However, SSD storage capacity does not meet the same levels that electromechanical spinning disk drives can.
  • All-flash Array (AFA) — An all-flash array, as the name implies, is a storage array composed of only flash memory drives. Also known as a solid state array (SSA).
  • Hybrid Flash Storage Hybrid flash storage combines both solid-state drives and spinning disk drives in ways that advantage from both. Hybrid flash arrays provide greater capacity than SSDs, and the performance capabilities of flash memory. The ratio of the two types of storage depends on the model, or the custom make of the array. One main use for hybrids is to allow teams to gradually replace existing spinning disk storage modules.

Flash storage benefits in the data center

Flash storage is utilized in data centers mainly to bolster performance, and is becoming more common as the price tag for flash memory continues to reduce. However, capacity limitation for solid-state devices still challenges data centers, and therefore will continue to use cheaper and more spacious spinning drives. In the data center, flash storage helps to:

  • Accelerate Application Performance — The main benefit of flash storage is super performance. Flash has faster access over electromechanical drives. Also, because of its capabilities to access data randomly, flash is exceptionally flexible for many applications, and helps to bolster VM creation in the cloud.
  • Improve Data Center Economics — Overall, adding speed and performance improvements into the data center improves its economics. Flash storage gives IT teams options in architecting storage solutions in the data center, when performance is needed flash can be added, when capacity is needed, storage can be built as hybrid, increasing capacity, and reducing costs.
  • Future-Proof Infrastructure — Two technologies in flash storage help companies to future-proof their infrastructure. First, hybrid flash storage mixes, in custom ratio, flash storage with traditional HDDs. This allows the use of both, and lets IT teams migrate their older systems easily to flash-based systems. Secondly, flash systems can support cloud integration workflows, which make it more convenient to begin adopting cloud elements, and eventually migrating to the cloud and a VM environment.

Flash file systems

Because flash memory lifespan depreciates faster than other storage devices, specifically designed flash file systems are used to extend that life by managing read and write operations different than would be for other storage. Technically this is achieved through the use of a memory technology device (MTD) layer. The MTD provides the abstraction layer between applications and hardware drivers. Through this, when flash storage is updated, a fresh block is written over, and file pointers are remapped to accommodate the change in data. At a later time, when memory management determines that it is most economical, it will then rewrite over older used blocks. Essentially, fresh flash memory will become full before rewrites are considered in an attempt to help extend life. This wear leveling method, however, does not apply to flash memory found in most popular removable devices, such as USB sticks, MMCs, SD cards, and CompactFlash memory, and instead these devices use a flash translation layer (FTL) and block storage. FTL metadata is stored in the flash space. The risk this poses is that the portions of memory that the mapping table resides on may wear out before the rest of the device. This risk is less so for enterprise flash storage which takes measures to ensure mapping tables are protected from wear, such as by allocating extra space for spares.

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