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Key-value flash targets more efficient data storage

We look at key-value storage, which promises much greater I/O efficiency and longer flash drive lifespans, but may be constrained by limited use cases and lukewarm productisation efforts

Imagine flash storage that stores data in exactly the format used by applications. That’s what’s promised by key-value flash media, as envisaged by at least one big drive maker, some researchers and startups, and in the NVMe Key-Value command set.

Productised manifestations of key-value storage are more than thin on the ground, however. There has been research around the subject, and we’ve seen the development of a command set for key-value in NVMe, as mentioned.

Meanwhile, in 2019, Samsung announced a prototype key-value drive, which got built into a spin-out called Stellus with plans for a key-value storage array, but this seems to have been consigned to the where-are-they-now file. More recently, startup QiStor floated plans to productise storage software and FPGA chips for key-value storage, and claims it can be a big market opportunity.

The idea is that by retaining data in key-value format, it’s made massively more efficient, speedy, energy-efficient and durable compared with the existing multi-layered input/output (I/O) process.

Currently, applications and hosts must translate storage I/O into logical block addressing (LBA) at drive level so that data can be located during read/write operations. That’s a data addressing method that goes back to the origins of spinning disk hard drives and their LBA modus operandi. And so, developers of key-value stores noticed inefficiencies in I/O that resulted.

In other words, right now, if an application interacts with a key-value database, it must talk to that database then translate key-value addressing via the host file system and into LBA-speak to find the physical location of data on disk. That process contains a heap of steps that could be removed to make it more efficient.

But also, logical block addressing brings other inefficiencies that key-value storage can remove.

Read more about key-value data stores

  • NoSQL database types explained: Key-value store. Learn about the benefits and detriments of utilizing a key-value store -- a simply designed NoSQL database that can potentially improve data processing speeds and scalability.
  • How does Kubernetes use etcd? Etcd is a lightweight, highly available key-value store accessible to each node in a Kubernetes cluster. Find out how etcd works and learn how to use it inside Kubernetes.

Flash storage suffers from poor durability as a result of erases and rewrites. Such activity is amplified because every time data is overwritten – to blocks a different size to LBA blocks – it has to be erased, moved and written elsewhere.

That need becomes more pressing as the device fills up so a single write to disk may result in multiple writes (known as garbage collection) as data is moved around. All of which creates wear, and shortens drive lifespan.

By contrast, key-value storage allows the application to talk directly to media with no need for translation through the OS, the file system and to media LBA.

That’s because key-value storage doesn’t need to know what physical block to look for to find what it wants. Instead, key-value storage manages placement of data and knows where values reside. The host, OS and file system don’t take part in the process. If a value is sought, the device looks through its internal mapping tables to find where its key is held.

Key-value is a widespread and strongly emerging way of storing data found, for example, in the JSON format, in the etcd datastore in Kubernetes, as a data type in JavaScript and Python programming languages, and is the basis of NoSQL databases.

In key-value, the key is the name of a variable and the value is its value, or values. Keys and values can be of any length and of different data types – eg, numeric, character, even images or sound files – and can also be nested, so a key may have a value that is another key, with its own values.

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