I'm putting together the 'de facto' advice for a selection of high capacity hard drive users; DataHoarders, Plex users, unRAID users, Software Raid and Hardware Raid, CCTV and NAS users. - your feedback and comments are welcome so I get this 100% correct, but this is opinionated from all the info I've assimilated. Many people would prefer direct answers instead of 'it depends' too much imo.
My first hard drive was 21MB, so that should age my general computer use experience, I'm typing this in Linux (admittedly Pop!_OS), use Plex & Jellyfin on my unRAID system and have built many a PC along with specced more for business and have used more NVRs than I can count. I've researched this a lot over the last 7 weeks, this is my advice:
Golden Rule: all things equal - cost, storage capacity etc. just buy CMR. Failing that look to the below
unRAID Users: CMR for Parity disk, At least one CMR Data, SMR for others, caveats!
Plex Users: SMR, it's cheaper for more storage usually - read the side Note!
DataHoarders: CMR at all costs
Software Raid Users: CMR at all costs
Hardware Raid Users: CMR at all costs
Disconnected Backup Users: SMR for up to 10 years backup or CMR for more recovery options later
NAS Users (Home/Small Business File Sharing): Generally CMR, SMR with caveats
NVR/Surveillance Users: CMR preferred, SMR potentially usable
Here's a quick summary table for easy reference and why - don't skip the golden rule above though!:
| Use Case | Recommended Drive Type | Why? |
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| DataHoarders | CMR | Long-term recoverability, reliability |
| Plex/Media Servers | SMR (usually) | Cost-effective for WORM, reads unaffected |
| unRAID (Parity) | CMR | Avoids critical write performance bottlenecks |
| unRAID (Data) | CMR (SMR OK, but problems later) | Acceptable with cache, especially for media, long rebuild times though with SMR so CMR is safe choice |
| Software RAID (ZFS, etc.) | CMR | Avoids rebuild issues, dropouts, poor performance |
| Hardware RAID | CMR | Avoids rebuild issues, controller timeouts |
| Disconnected Backups | SMR (Conditional) | Cost savings, acceptable for infrequent writes |
| NAS (General File Sharing) | CMR (preferred) | Handles mixed workloads better, RAID safety |
| NVR/Surveillance | CMR | Consistent performance for continuous writes |
Explanations
Super Quick Intro - What is SMR and CMR in general - if you know, just skip this bit
All the drives you had up until about 2015 (earlier in enterprises) were 'CMR', think of CMR as 'organic food', before we had all the pesticides, it was just 'food'. Then a new technology came along, called SMR (or pesticides in our analogy). This means instead of the data being written on the disk in nice orderly lines of data like an Olympic 400m track, they 'overlap' each other, that's what the S in SMR is, shingled, like on your roof, the tiles overlap each other, or fish scales overlapping each other. So now we have SMR, which in today's supermarkets is just 'food', and if you want the 'original food', it's called 'organic food', if you want the original not so complex technology, it's called CMR!
CMR - Conventional Magnetic Recording: what we always had, data written in distinct, non-overlapping tracks on the hard drive metal platters. Writing to one track doesn't affect its neighbours.1
SMR - Shingled Magnetic Recording: 'new' but not necessarily better technology where data tracks partially overlap like roof shingles. This allows tracks to be thinner, increasing data density – meaning more storage capacity in the same physical space.
The number one, main drawback for SMR: when writing data to an SMR drive that overwrites or updates existing data the drive must read the data from the overlapped track(s), combine it with the new data and then write all of that data back to the platters. This read-modify-write cycle takes way longer than a simple write operation on a CMR drive.
SMR Drives are like packing a suitcase: You're packed, ready to go, only to find the power adapter you've already packed for Europe was the wrong one. You have a choice, write a new file - slide the correct power adapter in the little outside pocket on your case (which is just like a cache) or update an existing file - open the whole case, dig out the items, find the wrong adapter, put the right adapter in its place, and re-pack the other items on top. That is the 'read-modify-write' cycle! If you placed the adapter in the cache, then later in lounge when you're just waiting around, you can do the whole re-packing thing to keep that little pocket empty, but what if you need to change more than just a power adapter, what if you packed for the wrong weather too, your side pocket (cache) would fill up, you'd have no choice but to just get on with the big switch around, no matter how late you're going to be for the flight.
SMR Cache is limited, that's why it's called a Cache!: on drive managed SMR (what we'll all be buying unless you've space for a datacentre in your loft) has a limited size. If you perform sustained write operations (like copying huge files, rebuilding a RAID array, or continuously recording video), this cache will fill up completely. Once the cache is full, the drive has no choice but to perform those slow read-modify-write operations directly into the shingled area as new data arrives. This causes a huge drop in write performance, often called hitting the "SMR performance cliff". Read performance of SMR, is more or less the same as CMR, because reading only involves the top layer of a shingle.
For Home Use, this is ok: Under general 'home' use, the cache can be big enough, so when the disk is idle, it will decide to do this extra work, and you won't know anything about it.
SSD Side Note: many are confused if they should buy an SSD or NVMe for some use cases, I've ruled that out, we're talking large data volumes here, at affordable rates, for storage and occasional use, therefore spinning disks are currently the best medium. Buy SSDs for your cache drives though!
Acronym Soup of CMR, SMR, HAMR, MAMR and more
PMR (Perpendicular Magnetic Recording): is the main fundamental recording method used in nearly all modern HDDs. It's not about track layout, where as CMR vs. SMR is about the track layout and how they are physically placed on the disk.
CMR (Conventional Magnetic Recording): Tracks are separate, like lanes on a motoreway. Better for frequent writes.
SMR (Shingled Magnetic Recording): Tracks overlap, like roof shingles. Allows higher capacity but can slow down sustained writes.
Newer technologies like HAMR and MAMR are assist technologies that can be built on top of either CMR or SMR track layouts.
CMR and SMR with assisted technologies breakdown
| Technology / Acronym | Primarily CMR (Non-Overlapping) | Primarily SMR (Overlapping) | Can Be Implemented as Either CMR or SMR | Underlying Method / Enhancement |
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| LMR (Longitudinal) | ✔️ | | | Older Recording Method (Pre-SMR) |
| PMR (Perpendicular) | | | ✔️ | Current Dominant Recording Method |
| CMR (Conventional) | ✔️ | | | Specific Non-Overlapping Track Layout |
| SMR (Shingled) | | ✔️ | | Specific Overlapping Track Layout |
| DM-SMR (Device-Managed) | | ✔️ | | SMR Type (Managed by Drive) |
| HM-SMR (Host-Managed) | | ✔️ | | SMR Type (Requires Host Control) |
| HA-SMR (Host-Aware) | | ✔️ | | SMR Type (Hybrid Management) |
| EAMR (Energy-Assisted) | | | ✔️ | Umbrella term for Write Assist |
| ePMR (Energy-Enhanced) | | | ✔️ | PMR Enhancement (Can be CMR or SMR) |
| MAMR (Microwave-Assisted) | | | ✔️ | Write Assist (Can be CMR or SMR) |
| HAMR (Heat-Assisted) | | | ✔️ | Write Assist (Can be CMR or SMR) |
[Thanks to u/MWing64 for pointing out errors in a previous version]
What you should buy for your use case
DataHoarders: Buy CMR at all costs
Why? If you're a datahoarder, you want your data to last, a llloonnggg time, way past the 10-15 year mark. If you're archiving the personal files of your grandfather or scientific research data, we don't want this to just last, it should be recoverable. assume we're 20-30-50 years in the future, the current 'latest technology' of HAMR, microwave, laser and who knows what technologies will have faded into the past. All the generally shingled data storage is going to be more difficult to recover when presented with just the physical metal platters extracted from that 3.5" case. If we're left with just that, we should make it as simple as possible to recover; and that means CMR not SMR.
No, there is no direct evidence saying SMR the technology itself fails more often, well, it's debated and thrown around, but having an SMR driv...
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