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SMR disk trap, CMR vs SMR on the SGdata channel

TechEkspert 18615 11

TL;DR

  • It compares CMR and SMR HDD recording, using an old 2GB drive and SGdata channel material to question whether SMR is worth choosing.
  • CMR stores non-overlapping tracks, while SMR overlaps tracks and relies on background corrections because the write head is wider than the read head.
  • The article warns write speed could drop from ~100MB/s to 15-40Mb/s, and in extreme cases to 10-20Mb/s during heavy overwrite workloads.
  • The conclusion is strongly anti-SMR for home NAS, RAID, encryption, deduplication, and CCTV-style cyclic overwriting, with CMR preferred instead.
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  • Reading the material the inside of an old 2GB HDD I remembered the material from the SGdata YT channel comparing the CMR and SMR recording methods used in HDD drives. Video from the SGdata channel below.

    CMR (Conventional Magnetic Recording) - data is recorded on magnetic tracks next to each other, the tracks do not overlap and the recordings do not affect adjacent tracks.

    SMR (Shingled Mgnetic Recording) - the tracks partially overlap each other (shingled magnetic recording), the data tracks are thinner so you can fit more data in the same area as in CMR. However, we will learn from the material that this method of recording may generate problems.

    SMR complicates the write operation, the write trace is wider than the read trace. Modifying data requires correcting previously saved data. According to the author of the material, new data will be saved by the disk "in the background" in a free space, and the disk software will correct the overwritten data during idle time.

    The material highlights the situation when the disk surface is completely written, then SMR may have a problem with writing new data to the free space. Additionally, what will happen if there is a power outage (USB portable drive) while corrections are being made by the drive? It depends on how the disk software was written.

    I have several hypotheses regarding SMR.

    1. Significant drop in write performance in certain cases:
    I noticed that SMR drives are also available for home NAS.
    What happens when data is saved/overwritten from several computers to such a home NAS?
    (e.g. holiday photos or a backup of a laptop connected to the home network)
    At some point the SMR drive must find time for corrections, if the writing is continuous and the amount of recorded data is too large, in my opinion the drive will force the transfer speed to be reduced to deal with internal correction procedures. Continuous sequential recording is a good scenario for a mechanical HDD (few head movements), which allows for fast recording. However, in SMR it seems that such a sequential write/overwrite will turn into a continuous skip of the write correction head, i.e. it will be a random write. The more write corrections (e.g. overwriting old backup files of our laptop), the greater the number of I/O operations generated by internal mechanisms, I suspect that the write speed may then drop from, say, ~100MB/s to 15-40Mb/s.

    2. Problems when working in a RAID group:
    Working in a RAID group may, in my opinion, worsen the effect of SMR delays, each disk has its own life and during adjustments it slows down the operation of the entire group. Working in RAID often means allocating the entire disk capacity and NAS software manages snapshots, spaces shared as logical entities relative to the physical structure of the disk. It is possible to save the entire HDD capacity (expanding the RAID group with additional disks, rotational backups, etc.).

    3. Problems with encryption, compression, deduplication:
    In my opinion, these may be further mechanisms causing multiplication write operations (need to modify data blocks) and the previously mentioned write speed values may, in my opinion, drop even to 10-20Mb/s in extreme conditions.

    4. CCTV monitoring, cyclic saving/overwriting of HDD in its entirety:
    according to In my opinion, SMR should not be used for such applications.

    What do you think about these observations?
    is it possible?
    am I wrong?

    Some manufacturers did not clearly communicate the use of SMR:
    https://www.benchmark.pl/aktualnosci/western-...je-liste-slabsych-dykow-hdd-z-zapisem-sm.html

    After reading the video materials, would I choose SMR when choosing a drive?
    NO.

    What is your opinion on this, would you choose an SMR or CMR HDD?

    Material from the SGdata channel:



    Cool? Ranking DIY
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  • #2 20279230
    Rack70
    Level 11  
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    TechEkspert wrote:
    What is your opinion on this, would you choose an SMR or CMR HDD?

    Some time ago I tried to identify the topic, I wanted to buy an HDD, of course in the CMR version. It is quite difficult to find information whether a given model was manufactured using CMR or SMR technology. I reached, among others, to such lists (in 2021):
    SMR disk trap, CMR vs SMR on the SGdata channel

    SMR disk trap, CMR vs SMR on the SGdata channel
    SMR disk trap, CMR vs SMR on the SGdata channel
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  • #4 20280461
    Shadowix
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    Rack70 wrote:
    It is quite difficult to find information whether a given model was manufactured using CMR or SMR technology.

    Well, my first result in Google after entering "cmd disk list" is difficult to find and it took me 5 seconds :)

    Of course, only CMR drives are used for "real" (i.e. professional) NAS systems. SMR drives are cheaper due to greater data density (fewer platters), despite additional software. Where high availability and performance are also required, SMR drives will not work, precisely because of the additional operations they have to perform themselves, which reduces performance. Additionally, there is an even bigger problem with recovering data from such a disk...
  • #5 20280507
    Rack70
    Level 11  
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    Shadowix wrote:
    Rack70 wrote:
    It is quite difficult to find information whether a given model was manufactured using CMR or SMR technology.

    Well, my first result in Google after entering "cmd disk list" is difficult to find and it took me 5 seconds

    CMR, not cmd, but ok. Today it is not a problem, because the topic has been publicized. It wasn`t that simple a year or two ago.
  • #6 20283583
    pawelr98
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    Large drives are always CMR, SMR are for "small" capacities, as shown in the tables. For manufacturers, small drives are less than 8TB.

    This is due to the fact that large drives are intended primarily for servers, where such SMR games would not be possible. Strictly high-capacity consumer drives are usually "rejects" from server lines.

    Not to mention the fact that the best price per GB for HDD is currently around the capacity of, as I remember, 12TB, and a year or two ago it was 8TB.
    1/2/4TB drives are generally not very profitable, the price per GB is often 2 or more times higher.

    It is not very profitable for manufacturers to make consumer drives with such small capacities, so they start trying to find SMRs to reduce costs, and the consumer still accepts them. Meanwhile, the best goes to the professional market where sales and, I suspect, margins are much better.
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  • #7 20292698
    Anonymous
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  • #8 20750829
    kaleron

    HDD and data recovery specialist  
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    TechEkspert wrote:
    Additionally, what will happen if there is a power outage (USB portable drive) while corrections are being made by the drive?
    - firmware problems are the most common causes of failure of these drives.
    TechEkspert wrote:
    1. Significant drop in write performance in certain cases:
    - this is a very typical symptom when you run out of space where data can be saved freely and with impunity. Housekeeping takes time until the disk is unable to handle write requests. The type of file system used also matters. In addition to saving the files themselves, metadata operations are also performed, e.g. NTFS, in which basically the entire file is described in one record. MFT is in this respect better than systems from the FAT family (we will usually have exFAT here), where the file description requires an entry. in the directory and in the file allocation table. In any case, it is not a coincidence that SMR drives have larger buffers than conventional ones.

    TechEkspert wrote:
    2. Problems when working in a RAID group:
    - here it also depends on the type of matrix. RAID1, it`s a mirror. But yes, a drop in write speed on a single disk will slow down the entire array.


    TechEkspert wrote:
    Problems with encryption, compression, deduplication:
    - but also copy-on-write systems... there are many pitfalls here. Originally, these were disks intended for archiving - save once and then read, if necessary...

    TechEkspert wrote:
    CCTV monitoring, cyclic saving/overwriting of the entire HDD: acc. In my opinion, SMR should not be used for such applications.
    - in general, I avoid SMR for all applications. The best use of SMRs is as a parts donor, because they are also subject to mechanical failures. Especially slim constructions.

    pawelr98 wrote:
    large drives are intended primarily for servers, where such games in SMR would not be possible
    - that`s not the kind of balls that go there. Consumer SMR drives are without exception DM - Disk Managed. This means that the disk firmware is 100% responsible for managing the translation of LBA to physical addressing. In the case of server solutions, you can also find HM (Host Managed - where the addressing translation is handled by computer software external to the disk(s)) and HA (Host Aware - where the responsibility for addressing management is divided between the disk and the host). I don`t know to what extent these solutions have been accepted in practice, but in their case, in order to properly arrange the addressing, the disk itself is not enough - you need to have the entire computer and the admin trying to save the situation doesn`t mess anything up.

    cefaloid wrote:
    ssd/nvme
    - they also have their problems and are far from always the optimal choice.

    cefaloid wrote:
    We have a few overlapping paths there and then a break so that the overwrite operation is limited to a few additional reads/writes.
    - usually the sizes of SMR zones are counted in tens of MB. The problem is that often incoming data is located in multiple zones, requiring much larger areas to be overwritten than with conventional writing, which would easily kill write performance and force combinations with the second level of the translator subsystem.
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  • #9 21380259
    r70
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    I have been using several Seagate SMR 3.5" 8TB, 6TB, and 2.5" 1TB and 5TB drives since 2019. Mostly the drives were to be used for me to back up data from a Synology NAS server. Backup is done with file fragmentation, due to deduplication, encryption, compression and saving multiple versions with retention of the oldest. I bought all the drives as USB and they were in NTFS format as standard. The first drive was a total failure - SMR drives were just entering the range and no one deigned to point this out. It was a failure - the transfer rate quickly dropped to a few KB/s or even zero. The battles with Seagate tech support were to no avail - constant pushing and no concrete answer; they wouldn't even admit that the 6-8TB Barracuda (not pro) drives were SMR drives.
    I experimented with NTFS, exFAT, EXT4 and each time the drive was virtually unusable. I finally checked how it would be with BTRFS - because it seemed to me that COW might turn up the situation. And it was a crapshoot. After setting up BTRFS partitions on these drives, they can write virtually any size of data without stuttering, without practically stopping to rewrite data from buffer to SMR space. Their advantage, however, is that despite the fact that they spin only about 5-5.5K revolutions, they can read data quite quickly (about 130-190MB/sec, because often the head can read 2 tracks in parallel) - which is more important for restoring backups than slower writing.
    Since I came to this conclusion, I have been systematically buying these drives whenever I have a need and there is a promotion (I bought the 8TB drives cheapest probably under 500PLN).
    On the other hand, I haven't tested any WD drives with this technology - and I'd love to see how their 2.5" 4TB drive works with BTRFS, for example (5TB isn't in WD, I think?).
  • #10 21380656
    Kris52
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    r70 I have such an external 2.5" segate 2TB or 4TB. It finished my patience while creating the disk image.The disk went to the drawer. If writing to the btrfs partition doesn't slow down that's good news. I will test
  • #11 21381001
    TechEkspert
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    How can Btrfs affect the operation of the SMR?
    I think with disk operation when it cyclically fills up with data, the oldest data is erased and new SMR writes will always be troublesome.
    A backup repository scenario or CCTV video recording is unlikely to want to work with SMR.
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  • #12 21381181
    r70
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    It's not that SMR drives with BTRFS don't slow down. They do have variable write speeds, but the average write speed for portions of data written at a time of 0.8-2TB is for example for Seagate 2.5" 5TB - 18-25MB/s (I've never had a lower speed) while for 3.5" 8TB it's 35-80MB/s. Of course you can imagine higher speeds, but comparing this to desktop drives in the 5000 RPM class and smaller capacity (0.5-4TB because I have such in CMR recording technology) it is on average about 20-30% slower. In 2.5" drives you can see the performance advantage of a 1TB drive over a 5TB drive, and in 3.5" drives 8TB mad 6TB.
    However, if someone wants to create a disk image urgently (e.g. to secure data as soon as possible), it's better to use a disk from a fast drive with a classic write.
    @TechEkspert ; I would definitely not install an SMR drive in a recorder, or any other solution where a fairly linear write performance is a must.
    The point is that while with NTFS, exFAT or EXT4 formats these drives become useless if they don't have very long rewrite intervals and the single large portions of data written (i.e. CMR buffer size) are relatively small, with BTRFS they are suitable for many applications as they operate with a higher average write speed and efficient read performance. For server data backup, they are economically justifiable :) .
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Topic summary

✨ The discussion centers on the differences between CMR (Conventional Magnetic Recording) and SMR (Shingled Magnetic Recording) technologies in HDDs, highlighting their operational characteristics and practical implications. CMR records data on adjacent, non-overlapping tracks, ensuring stable write and read performance, making it preferred for professional NAS and server environments. SMR overlaps tracks to increase data density and reduce manufacturing costs, especially in smaller capacity drives (under 8TB), but introduces complex write operations due to wider write traces and background data rewriting, which can degrade performance and complicate data recovery. SMR drives often have larger buffers to mitigate these issues but still suffer from slower write speeds and firmware-related failures when free space for background operations is limited. Use cases with mostly static data or sequential writes, such as backups or archival storage, may tolerate SMR limitations, whereas workloads requiring frequent random writes or databases are unsuitable. File system choice impacts SMR performance; BTRFS with copy-on-write can improve write behavior compared to NTFS, exFAT, or EXT4, though variable write speeds remain. Seagate SMR drives (including 3.5" 8TB, 6TB, and 2.5" 1TB and 5TB models) were specifically noted for performance issues and lack of clear labeling, causing user frustration. Large capacity drives (above 8TB) are typically CMR, targeting professional markets with better price per GB and reliability. Overall, SMR is a cost-effective solution for consumer-level storage with mostly sequential writes but is not recommended for high-performance or critical data environments.
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FAQ

TL;DR: SMR HDDs can drop from 150 MB/s to 15 MB/s writes—“housekeeping takes time until the disk is unable to handle write requests” [Elektroda, TechEkspert, #20278988; #20750829]. Why it matters: Picking the wrong platter tech cripples backups, RAID, or CCTV storage.

Quick Facts

• CMR tracks never overlap; SMR tracks overlap ~10 % for 10–20 % higher areal density [Seagate, 2023]. • Typical SMR cache size: 128–256 MB vs. 64 MB on equal-class CMR drives [Western Digital, 2022]. • Sustained SMR write: 15–80 MB/s once cache is full; CMR equals 120–200 MB/s on same RPM class [Elektroda, r70, post #21381181] • Power-loss during SMR “background reshingle” may corrupt pending data blocks [Elektroda, TechEkspert, post #20278988] • Drives ≥8 TB are "almost always" CMR; ≤6 TB consumer models often SMR [Elektroda, pawelr98, post #20283583]

How can I quickly tell if a hard drive model is SMR or CMR?

Check vendor spec sheets or crowd-sourced lists; many include “Record Type.” Search “ CMR” returns lists such as the 2021 tables shared in the thread [Elektroda, Rack70, post #20279230] If data is missing, run smartctl -i—some vendors embed "SMR" in the firmware string.

Why do SMR drives slow down after the cache fills?

SMR must rewrite entire shingled zones when any sector changes. Once the 128–256 MB cache fills, background “reshingling” starts, turning sequential writes into random I/O and dropping throughput to 15–40 MB/s [Elektroda, TechEkspert, post #20278988]

Is SMR acceptable for a home NAS?

Only if the NAS is for mostly-read archives. Frequent multi-user writes, snapshots, or RAID rebuilds trigger housekeeping stalls, harming availability [Elektroda, Shadowix, post #20280461] Experts recommend CMR for “real” NAS workloads.

What happens during a power cut while an SMR disk is reshuffling data?

Pending zone rewrites may be incomplete, risking metadata loss. Firmware bugs are the “most common causes of failure of these drives” under such events [Elektroda, kaleron, post #20750829] A UPS is strongly advised.

Do large capacity drives always use CMR?

Capacities ≥8 TB sold for servers are typically CMR because enterprise markets demand predictable write performance; sub-8 TB consumer lines often switch to SMR to cut platter count [Elektroda, pawelr98, post #20283583]

Can file systems mitigate SMR slowdown?

Btrfs’ copy-on-write reduced stalls for 1–2 TB backup bursts, keeping 2.5" 5 TB SMR drives at 18–25 MB/s average and 3.5" 8 TB at 35–80 MB/s [Elektroda, r70, post #21381181] NTFS and exFAT fared far worse.

Are SMR drives safe in RAID arrays?

Mixed arrays inherit the slowest disk. When any SMR member pauses for housekeeping, RAID 1/5/6 writes stall, extending rebuild times and risking a second failure [Elektroda, kaleron, post #20750829] Choose uniform CMR sets.

Edge case: What workload absolutely breaks SMR?

High-churn databases and CCTV recorders write near-continuously to the same zones. Users observed drives "virtually unusable," transfers collapsing to kilobytes per second [Elektroda, Anonymous, #20292698; Rack70, #21380656].

Is data recovery harder on SMR platters?

Yes. Shingled zoning complicates head swaps and logical reconstruction because physical sectors don’t map 1:1 to LBAs. Professionals report higher cost and lower success rates [Elektroda, Shadowix, post #20280461]

How do I maintain performance on an SMR backup disk?

  1. Keep at least 10 % free space to leave relocation room.
  2. Schedule large sequential writes, then idle the disk for housekeeping.
  3. Defragment only when space >20 %, and never run real-time deduplication. This minimizes cache thrashing and zone rewrites [Elektroda, kaleron, post #20750829]

Can SMR be useful despite the drawbacks?

For cold storage—archives written once, read many—SMR offers 10–20 % more capacity per platter at 5–10 % lower cost per GB [Seagate, 2023]. "I wouldn't rule out SMR if it doesn't show its flaws" [Elektroda, Anonymous, post #20292698]

What’s the price premium for CMR today?

Retail 8 TB CMR drives average ≈€160, while same-size SMR USB externals often dip below €100 during sales, as noted by users buying 8 TB for <500 PLN [Elektroda, r70, post #21380259]
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