When choosing hard drives for a media server, two main types of drive technologies are available – SMR (Shingled Magnetic Recording) and CMR (Conventional Magnetic Recording). Both offer advantages and disadvantages that are important to consider based on the intended use case and workload requirements of the media server. In this 5000 word guide, we will provide an in-depth look at SMR vs CMR drives, their technical differences, performance characteristics, and pros and cons for use in media servers to help you choose the best drive technology for your needs.
What is SMR?
SMR, short for Shingled Magnetic Recording, is a hard drive technology that was introduced in 2013. SMR drives aim to increase the storage density and overall capacity of hard disk drives beyond what traditional CMR technology can offer.
With SMR, the tracks on the platter are partially overlapped or “shingled” – this allows more tracks to be squeezed onto the disk platter, increasing overall capacity. The overlapping track design does come with some disadvantages which we’ll discuss later.
Some key characteristics of SMR hard drives:
– Higher storage density and capacity compared to CMR drives of the same physical size. SMR drives typically offer 20-25% more capacity.
– Data tracks are written in a shingled structure, overlapping adjacent tracks partially. This allows fitting more tracks onto the platter.
– Writing data requires rewriting overlapping tracks in each “band”, which has performance implications.
– Better suited for sequential write workloads instead of random writes.
– Often used for cold data storage, backups, archives where data is written sequentially.
– Lower cost per GB compared to CMR drives.
So in summary, SMR drives allow drive manufacturers to offer much higher capacities by overlapping the data tracks on a platter, at the cost of some performance penalties. The shingled design is better suited for sequential write workloads rather than random rewrites.
What is CMR?
CMR stands for Conventional Magnetic Recording. This is the traditional hard drive recording technology that has been used for decades before SMR was introduced.
In CMR drives, the tracks on the platters are written in distinct non-overlapping concentric circles, unlike the shingled structure of SMR. This makes CMR better suited for random writes, but limits the overall capacity compared to SMR.
Here are some key highlights of CMR hard drives:
– Tracks are written in concentric non-overlapping circles on the platter, as opposed to the shingled approach of SMR.
– Allows for full random read and write capability – well suited for random workloads.
– Lower storage density and capacities compared to SMR, typically around 20-25% less data can be stored.
– Higher cost per GB than SMR drives.
– Performs consistently well in both sequential and random access workload scenarios.
– No performance degradation over time.
So in summary, CMR drives use the traditional approach of writing non-overlapped circular tracks to the platter. This provides consistent performance for both sequential and random writes, at the cost of lower overall drive capacities compared to SMR.
Technical Difference Between SMR and CMR
Now that we have a basic understanding of the two technologies, let’s look at some of the key technical differences between SMR and CMR drives:
This is the most fundamental difference between the two drive types. In SMR, tracks are written in an overlapping shingled pattern which allows more tracks to be physically fit onto the platter. In CMR, tracks are laid out concentrically without any overlap.
CMR drives can directly overwrite any random location on the platter. SMR drives cannot directly overwrite due to the overlapping shingled tracks. To write data, SMR drives need to sequentially rewrite entire bands of tracks to avoid affecting adjacent tracks.
CMR drives offer consistent random and sequential write performance. SMR drives have good sequential write speed but poor random write performance due to the rewriting requirement.
SMR drives typically need a larger cache to help absorb bursts of random writes. CMR drives work well even with a small cache.
CMR drives work well for almost any workload – both sequential and random access. SMR is better suited for sequential data written in large chunks like backups, archives, cold storage.
SMR drives can suffer from performance degradation over time as out-of-place writes cause fragmentation in shingled bands. CMR drives have no such fragmentation issues.
So in summary, the overlapping shingled tracks of SMR drives significantly impact the write process and performance characteristics when compared to traditional CMR drive behavior.
SMR vs CMR Performance Comparison
Now that we’ve looked at the technical differences, let’s compare how SMR and CMR drives differ when it comes to performance benchmarks:
* Sequential means reading or writing data in consecutive locations on the drive.
* For sequential workloads, both SMR and CMR drives perform similarly. The shingled writing of SMR drives does not matter for large contiguous reads or writes.
* Benchmark results show SMR drives providing similar read/write throughput to CMR for sequential transfers.
* Random reads refer to reading data from random locations on the drive.
* Both SMR and CMR drives perform similarly for random read workloads. The shingled tracks have no impact on reads.
* Benchmark tests show similar IOPS and latency results for random reads on both drive types.
* This is where we see the biggest performance differences.
* Random writes involve writing data to random locations on the disk.
* SMR drives need to rewrite entire shingled bands during random writes. This requires large caches to buffer writes.
* CMR can overwrite any location so random writes have similar latency to sequential writes.
* Benchmarks show CMR drives providing up to 4-5x higher IOPS for random writes compared to SMR.
So in summary, random writes is where SMR struggles compared to CMR due to the sequential rewriting requirements. For reads and sequential writes, both drive types are comparable.
Pros and Cons of SMR vs CMR
Based on the technical differences and performance characteristics discussed so far, let’s summarize the pros and cons of each drive technology:
Pros of SMR Drives
– Higher storage density and capacity vs CMR drives
– Lower cost per gigabyte
– Works well for sequential write workloads like backups and archives
– High throughput for large contiguous reads and writes
Cons of SMR Drives
– Poor random write performance due to rewrites
– Requires larger cache to absorb burst random writes
– Performance degradation over time due to fragmentation
– Not well suited for heavy random workloads
– Rewrite amplification wears out drive faster
Pros of CMR Drives
– Excellent random write performance
– Consistent performance – no degradation over time
– Works well for both random and sequential workloads
– Lower rewrite amplification results in higher drive endurance
Cons of CMR Drives
– Lower storage density and capacities vs SMR
– Higher cost per gigabyte
So in summary, SMR drives provide high capacities at lower cost but are poor for random write workloads. CMR drives cost more but deliver excellent performance consistency and suitability for both random and sequential workloads.
Are SMR Drives Suitable for Media Servers?
Now we get to the key question – should you use SMR or CMR drives for your media server? Here are some considerations:
Media Server Workload Characteristics
Media servers like Plex, Emby, Jellyfin perform a mix of sequential and random reads/writes:
– Large sequential reads when streaming video files to clients
– Random reads fetching media metadata like subtitles, thumbnails etc.
– Random writes when updating libraries, metadata etc.
– Mix of large and small file writes when new media is added to libraries.
So media servers do have a decent amount of random IO in addition to sequential operations.
Performance and Stability
Random write performance and stability over time is critical for optimal media server performance. Issues like stuttering, buffering and crashes can occur if the storage can’t handle the workload.
CMR drives are better suited to handle the mixed random + sequential workload of a media server. SMR drives will struggle with random writes resulting in inconsistent performance.
Cost Savings vs Performance
SMR drives do provide significant cost savings over CMR, sometimes up to 30-40% lower cost per terabyte. However, the impact on performance may outweight the cost benefit for a media server workload.
If budget constraints are tight, SMR drives could work for smaller media servers with lesser concurrent streams and random IO pressure. For larger media servers supporting multiple concurrent streams, it’s advisable to spend a little more for CMR drives.
Drive Workload Considerations
If your media server also needs to handle other workloads like database servers, application servers etc, then SMR drives are definitely not recommended at all due to their poor random write performance.
However, if the server is a dedicated standalone media server only used for storing and streaming video files, SMR drives may provide decent performance if tuned properly.
Tuning SMR Drives for Media Server Use
If you do opt to use SMR drives for your media server due to budget constraints, here are some tips to get optimal performance:
– Use SMR drives in a RAID configuration to distribute load over multiple disks. Avoid using single large SMR drives.
– Use a hardware RAID controller with RAM cache to absorb random writes.
– Reserve 20-25% free space on the array to allow SMR drives to re-write bands efficiently.
– Enable disk write caching but with a protected cache or UPS, to avoid data loss on power failure.
– Isolate media files from OS/metadata. Store media on SMR array, OS and metadata on CMR SSD or NVMe drive.
– Schedule sequential/bulk writes like library scans, new media import etc during off-peak hours.
– Enable transcode/temp directories in RAM disks to avoid frequent SMR writes.
So while CMR drives are better suited for media servers, with careful tuning SMR drives may work for less demanding use cases. Thorough testing is recommended before deploying SMR storage for production media server workloads.
Example Media Server Builds With SMR vs CMR Drives
Here is an example build outline for a Plex media server using both SMR and CMR drives to illustrate the differences:
Entry Level Plex Server with SMR Storage
– Intel Core i3 CPU
– 8GB DDR4 RAM
– 120GB CMR SSD for OS/metadata
– 4 x 8TB SMR HDDs in RAID 5 (24TB usable)
– Hardware RAID card with 1GB cache
– Gigabit network connection
With careful tuning this could support 1-2 1080p streams reasonably well. RAID card cache will help absorb random writes. Leave 20% space free on the SMR array. Overall build cost is lower thanks to cheaper SMR hard drives.
Enthusiast Plex Server with CMR Storage
– Intel Core i7 CPU
– 16GB DDR4 RAM
– 480GB NVMe SSD for OS
– 512GB CMR SSD for metadata/transcodes
– 5 x 8TB CMR HDDs in RAID 6 (32TB usable)
– 10Gbps network connection
The all CMR drives provides great random + sequential performance to support multiple 1080p streams smoothly. NVMe SSD improves metadata/database performance. Overall cost is higher, but unhindered performance.
So for basic media servers, SMR provides a lower cost option if configured carefully. For enthusiast builds handling heavy workloads, CMR drives are worth the additional expense.
The choice between SMR vs CMR drives for media servers involves a tradeoff between cost savings vs performance. While SMR drives are cheaper per terabyte, their poor random write performance makes them less suitable for typical media server workloads with a mix of sequential and random IO. CMR drives cost more but their consistent performance profile better handles the demands of media serving.
For budget media builds, SMR drives tuned properly may suffice. But for enthusiast servers supporting multiple concurrent streams and high throughput workloads, CMR drives are highly recommended to avoid performance bottlenecks. As media server storage needs grow, it makes sense to invest in good quality CMR drives rather than troubleshoot issues caused by SMR drive limitations in the long run.