When it comes to types of server hard drives, there are so many variations out there that it can become challenging to keep track of all the considerations. "Can my server read a 4Kn drive?" "Can I mix SAS and SATA drives in the same machine?" "What about SSDs versus HDDs?"

While we've written extensively on hard drives, we thought it would be helpful to summarize all the types, formats, and interfaces in one place. Consider it our "Hard Drives Greatest Hits!"

SSD vs. HDD

We could write a whole blog post on SSDs vs. HDDs (oh, and we have). 

The abridged version: HDDs have been around for decades, and the technology has been improved and perfected. SSDs are a newer storage medium based on Flash technology (which is now ubiquitous in those little USB thumb drives).

Keep these very high-level principles in mind when considering between SSDs and HDDs:

• Performance. In terms of reading & writing and data transfer speeds, SSDs will always outperform HDDs.
• Volume & Cost. If your primary consideration is getting the best bang for the buck storage-wise, HDDs are a better solution. HDDs offer larger storage volumes at a price point that SSDs haven't reached.
• Mixing SSDs and HDDs in the same server. While you can mix SSDs and HDDs in the same server, you cannot have them in the same RAID array. A frequent configuration our customers use is to have the SSD run the OS and the HDDs for storage.

Advanced Format Drives (4Kn and 512e)

Advanced Format (AF) drives take advantage of larger data sectors to maximize storage volumes. Whereas traditional drives have 512-byte sectors that require more spaces between sectors (and consequently, volume on the drive is used up by empty space), AF drives minimize those gaps with larger byte sizes. Fewer gaps equal more volume on the drive for storing data.

Advanced Format Drives come in two configurations: 4Kn (4K = 4096 bytes; n = native) and 512e (e = emulation). 4Kn drives utilize 4096-byte sectors (hence, '4K'); 512e drives have 4K bytes per physical sector but maintain 512 bytes per logical sector. The advantage of 512e formatted drives is they will work in devices running an OS that does not support 4Kn sectored drives. 

Advanced Format drives are unquestionably a performance improvement over the 512-byte predecessors. However, proceed with caution. While 14^th Gen Dell PowerEdge servers and 10^th Gen HPE ProLiant servers are AF compatible, previous generations are not, especially when you account for RAID controller compatibility. (Read our blog post on 4Kn drives referenced below for a full breakdown!)

RESOURCES! ALWAYS! The above is a barebones explanation of Advanced Format Drives. If you want to deep-dive, check out our blog post: Compatibility Pain Points: 4Kn Hard Drives and Backwards Compatibility with RAID Controllers. 

SAS vs. SATA

Perhaps no other interface gets more customer questions than SAS vs. SATA. It's an understandable query since SATA and SAS connectors/drives look virtually identical to the naked eye (see below).

Here are some high-level SAS vs. SATA principles:

• SAS drives have a higher Mean Time Between Failure (MTBF) and faster data transfer speeds than SATA drives. Translation: SAS drives perform better.
• SAS drives also are more expensive than their SATA counterparts, around 10% (although that price difference decreases if you go the refurbished route!).
• Enterprise rack servers have backplanes that are SAS and SATA compatible. That said, there is the caveat of mixing SAS and SATA drives together in the same machine, specifically in the same RAID virtual disk (it cannot be done!).

You can check out our blog post on SAS vs. SATA drives for an in-depth analysis.

We would be remiss not to share our Hard Drive product page, where you can view all of TechMikeNY's in-stock hard drives!

CMR vs. SMR

Some customers have asked our sales reps before pulling the trigger on an order, "are your refurbished drives SMR or CMR?"

SMR (Shingled Magnetic Recording) drives are a type of drive technology that maximizes the drive's platter density. To put it in simple terms, 'Shingled' Magnetic Recording drives follow the same architectural principle as a roof's overlapping shingles, increasing the roof's surface area. The main advantage of SMR drives is higher drive volumes (due to their higher density). Most often, they are for very large drives used for NAS machines.

CMR (Conventional Magnetic Recording) drives are a more traditional hard drive technology that does not utilize a shingled or overlapping storage design.

A couple of main points to consider when it comes to CMR vs. SMR:

• SMRs are better suited for static high-storage and low heavy reading and writing. The technology that allows the drive to have a high storage volume also impacts the read & write capability. Often, if you see a drive with low cache specs, it is likely an SMR drive.
• CMR drives are more versatile and appropriate for traditional hard drive tasks involving data reading and writing.
• CMR drives are the vast majority of drives in the marketplace, and consequently, almost all of the refurbished drives TechMikeNY keeps in stock are CMR drives. (Although it was in the news a couple of years ago that manufacturers were sneaking more SMR drives into the market!)

Final Thoughts on Server Hard Drive Types

Hard drives are understandably a big support topic. At TechMikeNY, we believe an informed customer is a happy customer! Hopefully, with these high-level summaries (and deep-dive links), you can feel equipped with knowledge.

Here are more resources that may come in handy for your hard drive purchases:

• What Are the Quality Metrics We Use for Our Refurbished Hard Drives?
• RAID Do's, Don'ts, and Best Practices (We summarize many of the aforementioned hard drive compatibility pitfalls.)
• NVME SSDs (a helpful primer on NVMe SSDs, which are now ubiquitous in laptops and are making their way into Enterprise servers.)

 Do you feel we missed any essential hard drive topics? We'd love to hear from you! Leave a comment below!