You have probably already heard about shingled magnetic recording (SMR) drives, a development in HDDs that slightly overlaps each track (like roof shingles) to achieve higher density than conventional magnetic recording (CMR) drives. Achieving more tracks per inch – higher density – for HDDs has been a holy grail of drive engineering for decades, and results so far have been impressive, with the latest SMR drives achieving 20TB last year.
This ‘shingling’ leads to one big difference between SMR and CMR drives. In CMR drives, there are gaps between recording tracks that impact areal density since parts of the platter cannot be utilized. SMR drives don’t require these gaps. Instead the data is written sequentially and then overlapped with another track of data. In HDDs, the write head is larger than the read head. In SMR, two tracks are written overlapped, and the narrower read head can “read between the lines” and isolate each single track just like any other HDD. As with any drive, random reads are supported, however random writes are not possible in SMR drives since you can’t replace a bad roof tile without ‘unshingling’ all the others. Most importantly, SMR brings big benefits for the right type of application where writes are sequential in nature, including video surveillance, online archives, cloud storage, storage for regulatory compliance and big data storage.
The requirement for sequential writes has led to the development of two kinds of SMR drives. The first is drive-managed, where the drive itself handles appending or overwriting the overlapped tracks, appearing just like CMR drives to the host system and OS. This enables seamless integration for mobile and client use cases.
Host-managed SMR, on the other hand, utilizes specialized drivers and requires modifications to the file system and host application to ensure that the writes are sequential. Benefits are outlined below.
What does SMR mean for the data center?
Host-managed SMR drives deliver significant TCO advantages for data centers and hyperscale cloud operators who want the highest capacity drives and control how data is written to the drives for specific workload or application needs. The increase in density means that rather than having to build out more racks and cool more buildings, enterprises are able to substantially boost their storage capacity while retaining the existing footprint. This not only yields a better rack density, it also can have significant capital investment implications, eliminating the need to find a bigger facility or a new power source.
Thanks to Linux® support for zoned SMR drives and support for new drive commands ZBC (Zoned Block Commands) and ZAC (Zoned-device ATA Commands), data centers are taking advantage of host-managed SMR drives for applications such as archival and object storage where they can offer increased price-performance while vastly reducing the time to access archived data versus older technologies like tape.
Also, the technology behind zoned block management, or zoned storage, means both host and storage applications can intelligently place data at scale to take full advantage of the highest available storage capacities, typically with SMR HDDs and the recently ratified zoned namespaces (ZNS) standard for NVMe™ SSDs. ZNS SSDs share common architecture with SMR HDDs in that both devices take advantage of host control of data placement and serialized writes. This commonality allows for a single software stack to support both HDD and SSD zoned storage devices.
Application Awareness Drives Gains
As organizations optimize their application stacks to take advantage of SMR HDDs, those organizations can immediately take advantage of the benefits of improving TCO and density. Modifying the software stack allows a forward migration path to future high-capacity host-managed SMR products. Investment today also minimizes incremental efforts for future SMR solutions, and gives customers a time-to-market advantage. This is a win-win for both data center and cloud providers who are always looking to do more with less.
Of course, these advantages do not come completely free. Enterprises must find those applications where sequential writes make sense, and the development community must uncover new takes on older applications like databases that benefit from the capacity gains that SMR brings.
Serving Storage Sequentially: SMRs as the Data Center Standard
The constant demand for higher capacity and lower TCO will make SMR HDDs the preferred option for the data center. Western Digital has been in the forefront of drive technology for decades, and already holds a prominent position in the SMR marketplace. Click here to learn more about SMR solutions for the data center.