noobie Loc: South Chicago

When purchasing a HDD these days, you might want to pay attention to what recording technology it is using. In the past, pretty much all drives used Conventional Magnetic Recording (CMR) where tracks are written side-by-side and do not overlap.

Beginning a year or so ago, all of the major HDD manufacturers began slipping Shingled Magnetic Recording (SMR) drives into their product lines --- WITHOUT telling anyone. With SRM, the tracks overlap much like shingles on a roof. The upside of this is greater track density which leads to using fewer platters and heads than CRM drives and then, ultimately, to high-capacity drives that cost less a lot less to manufacture. The downside is that SMR handles using/releasing free space in a complicated/inefficient way and in some applications that activity can create serious problems. If, for example, you are filling a backup drive by creating large backup images, deleting an old image and immediately writing a new large backup file, or if you are using a RAID array you'd be well advised to ensure any new drive you purchase is a CMR drive.

SMR does result in lower performance, but it enables cost savings that are attractive to some users, and if used in the correct types of workloads, those savings are worth the exchange of gaining access to deeper capacity. However, using SMR tech for desktop and laptop boot drives will likely remain a topic open for debate, as their underwhelming performance in sustained random write workloads could hamper performance in standard operating systems.

Considerable information, analysis, and discussions about this are easily discoverable with Google.

Longshadow Loc: Audubon, PA, United States

I have drives.
As long as they work, I'm fine.
Not worried about methodology.
Disk recording heads in the mid 70s were about 3/4 of an inch in size, now they are smaller than a tick.
This allows placing the tracks closer together and narrower tracks, requiring more accurate head positioning. Didn't seem to screw things up.

anotherview Loc: California

Thanks for alert and analysis.

no12mo

aphelps Loc: Central Ohio

Pro recorders were full track using the entire width of the tape for best sound quality. Then came stereo and the format changed to half track with left and right channels sharing the tape. Then with two sided casettes, the format became quarter track. As the recordable track size shrank the audio quality was reduced.

noobie Loc: South Chicago

Valid point about diminishing track sizes over time not causing problems, but the issues with SMR are way beyond that simple change.

The SMR overlapping-tracks architecture complicates the writing process since writing to one track also overwrites an adjacent track. If adjacent tracks contain valid data, they must be rewritten as well. As a result, SMR drives are divided into many append-only (sequential) zones of overlapping tracks that need to be rewritten entirely when full, resembling flash blocks in solid state drives. Consumer-level device-managed SMR drives *hide* this complexity by managing it in the drive's internal firmware, presenting an interface that deceptively looks like any other hard disk. While SMR drives can use *large* caches to help improve writing performance, continuous read/writing of data is slower than with CMR drives.

SMR is a good way to get more data into a smaller space, on a budget. But all this overlapping and rewriting results in much slower performance – also, likely much harder (impossible?) to ever recover data if your hard disk fails.

Guess my definition of "they work" differs from yours. As is often said these days, "Follow the science."

noobie Loc: South Chicago

Another take on explaining the issues with SMR --- the differences between CMR and SMR

Regardless of whether an HDD uses CMR or SMR, the read head only requires a small portion of the written magnetic track.

When new data is written on an SMR drive, the tracks are fully readable without impacting performance.

However, when the data on an SMR drive is edited or overwritten, the write head will not overwrite the data onto the existing magnetic track (like CMR does). Instead, the new data will be written onto an empty area of the disk, while the original track with the old data will temporarily remain. When the HDD becomes idle, it will enter a reorganization mode, where the old bits of data on the original track will be erased and made fully available for future use.

This reorganization mode must occur to completely delete tracks, making the idle time essential for an SMR drive. If an SMR drive is being used heavily for reads and writes, it will not have enough time to reorganize the magnetic tracks, causing the tracks with the old data to stay put temporarily. As a result, the SMR drive may need to write new data and reorganize the old track at the same time, resulting in a negative impact on the overall read/write performance.

EddieE Loc: Dallas, TX

There are two types of hard drives in the world:
1. Those that have failed.
2. Those that will fail.

Merlin1300 Loc: New England, But Now & Forever SoTX

OK - - I'll bite.
How do you differentiate CMR vs SMR ??
I've used WD Red NAS certified for the past 12 years.

noobie Loc: South Chicago

Well, it's getting really hard to find any information on the packaging and/or spec sheets for drives to determine which recording technology they use. The best bet is to either ask the manufacturer tech support directly about a specific model number drive or to Google something like "which Seagate hard drives use SMR" - of course, change Seagate to whichever manufacturer you are curious about.

Here's a link from last year that's a good starting place...
https://www.truenas.com/community/resources/list-of-known-smr-drives.141/

This link is specifically about WD Red drives - you may not be happy...
https://www.servethehome.com/wd-red-smr-vs-cmr-tested-avoid-red-smr/

Here's a list of WD, in general
https://www.extremetech.com/computing/309730-western-digital-comes-clean-shares-which-hard-drives-use-smr

Merlin1300 Loc: New England, But Now & Forever SoTX

Thanks - - I appreciate the links
I found that all but 1 of my 7 3TB WD Red drives (purchased a year ago for eventual use when my RAID arrays in my main production computer begin to show errors) are the EFRX = CMR type. Only 1 is SMR - so I guess I'm OK
I'll need to pay attention to this however when it comes time to replace the 4TB drives in my NAS and it's external USB-3 back-up array.

Bret Perry

Interesting!
How does one find out if it's CMR or SMR if they didn't tell us?