Enlarge /. The newer small drives with SMR equipment remain "red", while the CMR models all become "Red Plus".

Western digital

SMR where you least expect it

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Update 5:08 p.m. ET: pricing
Ars asked a Western Digital executive about pricing for the new Red and Red Plus lines. The first answer was, "In general, we expect prices for WD Red drives to be lower than those for WD Red Plus drives." When asked how the prices of the existing EFRX and EFAX models will shift in order to make red cheaper than Red Plus, I only replied: "I can currently only comment on the (previous)", followed by "WD" Red Plus will be available in August. "

Original story 7:34 p.m. ET
Last night, a Western Digital executive contacted Ars to share a blog post about their controversial Red Drives.

The company is taking a new brand initiative to clarify the technology used in its NAS drives. In the near future, "WD Red" will only mean hard drives with Shingled Magnetic Recording technology and "WD Red Plus" hard drives with conventional magnetic recording.

overview

This report is the latest in a line of hard drive manufacturers that integrate SMR technology into existing hard drive lines without telling customers.

In short, SMR hard drives generally perform well at low memory loads, with a lot of idle time between memory requirements. With more demanding workloads, however, they can fall catastrophically in the face. The ZFS file system, in particular, presents SMR hard drives with challenges that are difficult to deal with.

Although all three remaining major hard drive providers – Western Digital, Toshiba and Seagate – have "submerged" SMR hard drives in existing channels without informing customers, only Western Digital has done so with hard drives designed specifically for NAS or Network Attached storage was used.

Unfortunately for Western Digital, NAS users tend to be much more technical than general consumers – and they often hit their hard drives with much more difficult workloads than Western Digital appears to have tested or planned.

From red to red plus

The use of SMR technology in Western Digital Red is not diminishing – but in the future "red" will only mean SMR hard drives. The existing SMR models – WD 20/30/40/60 EFAX – retain their existing model numbers and their existing WD red branding. In the meantime, the CMR hard drives formerly known as WD Red – in sizes from 1 TB to 14 TB – are getting a new "WD Red Plus" logo and label, even though their model numbers remain the same.

Western Digital's new marketing for SMR-equipped Red drives marks them only for use with SOHO and clarifies that this means low-intensity operations with a lot of idle time in between and without ZFS. For small businesses, "intensive" or ZFS workloads there is the Red Plus line – which currently only means the older pre-SMR models.

There is also a Red Pro line for maximum performance applications. This line is unchanged – it existed before the SMR fiasco with the same branding and still exists with the same branding and models.

Understand SMR restrictions

The otherwise SMR hard drives have a fairly large CMR cache area and a 256 MB volatile RAM cache. Western Digital does not publish any details on the CMR cache area in its product data sheets. Typical estimates, as shown in this block sand file interview, range from 1 GB to 100 GB, depending in part on the size of the hard drive.

The CMR cache area on the drive behaves exactly like a CMR hard disk. If "downtime" occurs between storage requests, the drive firmware can spend this time reading data from the CMR cache and significantly reducing the amount of main memory space available for SMR. Once the data is permanently stored in the SMR zones, it can be read at approximately the same speed as it would have come from a corresponding CMR hard disk. SMR's performance restrictions are strictly tied to writes.

If you've never had enough writes at once to overflow the large CMR cache area and given the drive longer idle times to "breathe", you won't notice a difference in performance between CMR and SMR hard drives – although some NAS's case users have commented, "You can hear them running all the time." This relates to the garbage collection process, in which data is migrated from the CMR cache into SMR zones that occur in long idle times between processes.

Even if you run enough large writes at the same time to overload the CMR cache, Western Digital's SMR firmware generally does a surprisingly good job in our tests of transferring writes directly to the SMR zones. However, this good job requires that these writes are large, coherent writes – and that they are new writes, not rewrites of existing data. In order to change a single 4 KB sector in a 256 MB SMR zone, the firmware must read the entire 256 MB zone, then change this sector and then write out the entire 256 MB zone again.

Is the new branding enough?

The new branding is certainly a big step forward for more knowledgeable consumers who already know they don't want an SMR. The only thing you need to know is that "Red" means SMR and "Red Plus" and "Red Pro" mean CMR. The new branding replaces long tables with internal model numbers that reseller websites may not display accurately, even if consumers know which to use.

However, we are not sure whether the new, simpler branding will satisfy existing lawsuits against Western Digital. A US class action lawsuit claims that marketing an SMR hard drive as a "NAS" diskette is a false advertisement that can be implemented. The new branding is a big help for consumers who already know what SMR means and where its limits are – but they are unlikely to do much to educate consumers who are new to it.

Our use case analysis shows that SOHO workloads are usually based on short access times to the drives. This results in an extremely low average throughput (compared to the available throughput of the drive) and gives the DMSMR drive enough idle time to perform the necessary background operations, making it ideal for this application.

We broadly agree with the quote above from Western Digital's blog post announcing the new branding. The majority of consumers who buy small Synology, Netgear or other specially designed NAS devices are likely to use them intermittently with a small number of total users and mainly for large files such as digital photos, movies and music. For these consumers, an SMR-equipped Red is probably fine – they are unlikely to search the CMR cache, and even if they do, the SMR management firmware is likely to handle the direct writes quite well.

The real question for the future is how well does Western Digital's blog post announcing the new branding match the actual product details on the reseller websites. If there is no clear distinction between Red, Red Plus and Red Pro on the product pages themselves, the new branding may not reach many of the people who need to see it.

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