Dropbox was one of the first large cloud service provider (CSP) providers to deploy hard drives that use Single Magnetic Recording (SMR) to increase storage density in data centers. The company is looking forward to future technology and plans to be one of the first adopters of HDDs with heat-assisted magnetic recording (HAMR), so how will HAMR drives impact data centers? We have already made plans for what we will do and how we will need to prepare for its deployment.
In a surprisingly candid blog post, Dropbox shared some thoughts and experiences ahead of rolling out HDDs based on HAMR technology. It offers capacity starting at 30 TB and extending to over 100 TB in the future. To ensure predictable performance of these hard drives and maintain data center quality of service (QoS) requirements, the company will have to redesign its servers and introduce some changes to its infrastructure. .
Perhaps the most interesting point concerns vibration control and tolerance. Since HAMR aims to radically increase the areal density of hard drive platters, it is inevitable that the track density will also increase. Higher areal densities improve sequential read/write performance for HDDs, but the high frequency vibrations common in data center racks make the drives more prone to head positioning errors, reducing performance. Vibrations are caused by fans, nearby hard drives when performing seek actions, and rotational forces on HDDs, so the challenge for CSPs like Dropbox is to minimize the impact of vibrations on each drive. .The company plans to address its 7 vibrationsth generation servers by leveraging the HDD Dynamics specification developed by the Open Compute Project.
Eric Shobe, Hardware Engineering Manager at Dropbox, said in a blog post: “As we move into the next generation of HDDs, it will be important to focus more on this area. It is great to see some work already underway in the Open Compute Project (OCP) community. We plan to leverage OCP’s HDD Acoustical Surrogate, an industry standard specification for vibration testing — our 7th generation design. ”
Another characteristic of high-capacity hard drives in general is that IOPS performance per TB degrades as capacity increases. Once the HDD’s random performance per terabyte falls below a certain level (some say less than 5 IOPS per TB, the actual number will depend on your specific performance requirements), this drive will pass the Service Level Agreement. It doesn’t, so it doesn’t meet the QoS requirements. To address these issues, CSPs use less capacity per drive (i.e. buy smaller drives or pay for unused capacity) and have firmware implement command queuing. and delay bounded I/O (LBIO). (i.e. lower performance), use SSD caching (thus reducing HDD usage), or use hard drives that offer higher I/O performance. HDD manufacturers, on the other hand, are addressing the lower IOPS per TB performance by producing drives with two independent actuators that effectively double the IOPS per TB.
“We also anticipate eventually needing dual actuator drives to meet the IOP/TB requirements,” Shobe wrote. “Increased density can only be achieved if you only have one channel for I/O, but if you have two channels, the drive can sustain he IOP effectively doubles he .”
While the IOPS per TB performance degradation can be mitigated, I/O performance per server enclosure is another concern for CSPs such as Dropbox.
Dropbox Hardware Engineering Manager writes: “For example, in order for our Gen 7 servers to theoretically support more than 6 PB in a single enclosure, we had to rebuild our network to be able to evict and repair data at an acceptable rate. .”
In general, Dropbox is looking forward to adopting high-capacity HAMR HDDs in their data centers, but to use them efficiently, they plan to deploy 7 HAMR HDDs.th A generation server that addresses vibration and per-box I/O issues.
