Western Digital has been in hot water for months over its attempt to sell SMR hard drives into the WD Red product family. Red drives are explicitly intended for NAS (Network Attached Storage) devices, and as we’ve seen in several investigations, SMR drives from WD do not always perform adequately in that role.
Western Digital’s solution to the problem is to create a new tier of products, dubbed “Red Plus.” Going forward, WD Red will be a three-tiered system. All SMR hard drives will be sold as ‘Red,’, while the CMR drives that formerly populated the Red family will be rebranded as “Red Plus.” The Red Pro family will not change.
Personally, I would’ve preferred keeping CMR (Conventional Magnetic Recording) drives as ‘Red’ and labeling the new SMR drives something else, but WD wants to retain the fiction that it hasn’t just bait-and-switched the entire Red product family by dumping the onus to learn about the difference on its own customer base. Customers who currently own CMR WD Red drives will have to intuit the need to replace them with Red Plus drives when the existing models fail.
According to WD’s blog post on the topic, the drive-managed SMR drives it sells are intended for NAS devices with very low overall throughput and a great deal of idle time to perform background processing. Background processing is how SMR drives maintain acceptable performance while moving data in programmed read/erase cycles, not unlike those used by SSDs. For more details on how SMR drives work, please see our previous coverage here and here.
Western Digital states this problem occurred because “The explosion of data seen today has spawned a spectrum of NAS uses cases, as well as increasingly demanding applications.” I don’t find this to be an acceptable or credible explanation, and I don’t think you should either. The problem I have with WD’s statements on this topic is simple: It’s literally the manufacturers’ job to make certain that its purpose-marketed hard drives perform excellently in the hardware it is intended to operate in. ZFS not playing nice with SMR is very much a known problem. It just (somehow) wasn’t known to WD.
WD claims to perform extensive validation testing on various NAS arrays, which makes it sound like ZFS configurations might have just fallen through the cracks. But this kind of early evaluation is exactly what WD is expected to perform, and data from iX Systems — a vendor WD specifically references working with on its blog — shows that WD didn’t perform that validation process correctly. From iX Systems:
At least one of the WD Red DM-SMR models (the 4TB WD40EFAX with firmware rev 82.00A82) does have a ZFS compatibility issue which can cause it to enter a faulty state under heavy write loads, including resilvering…
In the faulty state, the WD Red DM-SMR drive returns IDNF errors, becomes unusable, and is treated as a drive failure by ZFS. In this state, data on that drive can be lost. Data within a vdev or pool can be lost if multiple drives fail.
WD has been shipping these hard drives since late 2018. Complaints have been stacking up the entire time. What WD appears to have done is to assume customers would magically know that their drive-managed SMR implementation had problems with ZFS. There was no prominent marketing material or guidance published by the company to guide people away from SMR drives and towards CMR if they intended to use ZFS, at least not until now. There was no specific data on the dramatic performance difference that can arise between SMR and CMR HDDs, as shown by ServeTheHome:
WD claims to be listening, but states, in the very next paragraph: “The DMSMR drives met all of our test requirements.”
The only thing that statement tells us is that WD’s test requirements aren’t thorough enough. Telling me “these drives meet test requirements” when the drives are failing in end-user deployments isn’t a defense, it’s an indictment. It should be noted that this issue has been assumed to impact all SMR drives in certain NAS arrays. WD is the only company selling SMR drives into these systems, but the firmware issues iX Systems raises means that some problems could theoretically be caused by (or improved by) firmware updates. This appears to be a complex question, however, and the fundamental way SMR drives perform write operations means they can’t match CMR drive performance in certain tasks. Firmware could improve things, but only to a certain point.
I don’t disagree with Western Digital’s claim that SMR drives can handle some degree of NAS workloads and configurations, but this problem should never have happened in the first place. If you intend to use ZFS, you’ll want to buy Red Plus or Red Pro drives — or maybe hard drives from a different vendor altogether.
Now Read:Western Digital Sued to Permanently Block SMR in NAS HDDs Red Alert: WD Sued for Selling ‘Inferior’ SMR Hard Drives to NAS Customers Western Digital, Seagate Are Shipping Slow SMR Drives Without Informing Customers: Reports