CMR vs. SMR Laborious Drives: What’s the Distinction?


Disassembled hard drive from a computer

Since 2015, onerous disk producers have produced a brand new form of force: SMR, which retail outlets extra information in keeping with disk however comes with some drawbacks in comparison to the normal garage manner, referred to as CMR. Every kind has execs and cons—let’s have a look.

Two Other Techniques of Storing Information on a Disk

Laborious drives retailer information in “tracks,” which might be round paths most often orientated in concentric rings at the best and backside surfaces of a difficult disk platter. Every onerous disk unit can include more than one platters, which permits the force to retailer extra information.

Traditionally, producers have greater garage capability in onerous disk fashions by way of both expanding the choice of platters within the force or expanding the write density at the disk. Up to now, the round tracks written to the disk by no means overlapped. The information garage business calls this “Perpendicular Magnetic Recording” (PMR) or “Standard Magnetic Recording” (CMR).

A track diagram of CMR vs. SMR in hard drives
A observe diagram of CMR vs. SMR in onerous drives. Seagate

Not too long ago, a brand new methodology for expanding write density referred to as “Shingled Magnetic Recording” (or SMR) has emerged. SMR drives write information the use of a distinct manner that partly overwrites up to now written tracks on a difficult disk platter. The producers use the analogy of roof shingles that partly overlap each and every different to provide an explanation for this system, which is the place the “shingled” a part of the identify comes from.

Whilst SMR drives building up capability for lower price (since the drives can use fewer platters than a CMR force on the similar capability), the way in which they paintings additionally comes with a velocity penalty. Whilst you reproduction information to an SMR force, the force quickly retail outlets the information in a particular cache space and makes use of idle time later to prepare it into shingled areas at the platter. Lengthy, sustained writes endure velocity consequences as a result of if the cache fills up, each and every time an SMR force overwrites a part of a prior observe, it will have to learn and re-write the “partly lined” underlying information as smartly. So SMR drives can carry out dramatically slower than CMR drives.

SMR’s gradual efficiency resulted in a controversy in 2020 and 2021 when other people discovered that producers have been promoting SMR drives with out labeling them (in each exterior onerous disks and inner drives), arguably promoting an inferior product with out caution consumers. A few of these court cases even resulted in a $2.7 million class-action agreement with Western Virtual in 2021.

So Is SMR Dangerous? Which Power Sort Must I Make a selection?

Whether or not SMR is dangerous or no longer is a subjective name. If you wish to have huge quantities of garage for much less cash and also you don’t thoughts the efficiency consequences concerned, an SMR force may well be an OK selection for you. Normally, a 16TB SMR force prices lower than a 16 TB CMR force, as an example. If you happen to use a force for infrequent single-disk backups, an SMR force may well be positive.

However beware: A big problem of SMR present in checking out by way of ServeTheHome is that the use of a gradual SMR force in a RAID array can put all of the array’s information in danger for longer as it takes a long way longer for the SMR force to get built-in into the array. So the use of SMR drives in a NAS with more than one disks might not be a good suggestion.

Thankfully, some producers reminiscent of Seagate have begun publishing information on-line that obviously displays which drives of their lineup use SMR or CMR era, despite the fact that maximum nonetheless don’t obviously label the drives as SMR or CMR whilst you acquire them from a store. Nonetheless, with this knowledge to your palms, you’ll be able to make a extra knowledgeable buying choice—reminiscent of deciding on a CMR force to make use of in a home-built exterior USB force.

General, we advise buying CMR drives every time imaginable because of the efficiency problems with SMR drives. However it stays a private and price range selection relying in your scenario and the way you utilize the force. Excellent good fortune!


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