Hard Drives

What a Hard Drive Is Still For

A hard drive stores data on spinning platters, so it is slow at the small scattered reads that Windows and games depend on. What it gives you instead is space: a terabyte on a hard drive costs roughly a quarter of what it costs on an SSD, and the gap grows at the large sizes.

That makes the sensible layout for most PCs an SSD for Windows and the games you play, and a hard drive alongside it for recordings, photos, project files, backups and the games you are not playing this month. For a full comparison with live prices, see SSD vs HDD.

CMR and SMR: the Spec That Matters Most

Recording type describes how the drive writes tracks to the platter. CMR (conventional) writes them side by side. SMR (shingled) overlaps them like roof tiles, which fits more data on a platter but means the drive must rewrite neighbouring tracks when you change data in place.

In normal desktop use an SMR drive feels much the same. Under sustained writing, a long file copy, a backup that runs for hours, or a RAID rebuild, it can slow sharply and stay slow. That is why NAS makers ask for CMR. We mark a drive CMR or SMR only where its maker states it, so a drive shown as not confirmed is unknown, not SMR. For what the difference costs in practice, with the split across the drives we track, see CMR vs SMR.

Spindle Speed, Cache and Workload

Spindle speed is how fast the platters turn, usually 5,400 or 7,200 RPM. Faster spinning means shorter waits for data to come round and higher transfer rates, at the cost of a little more noise, heat and power. Note that some makers label a drive “5,400 RPM class” when the spindle actually turns faster.

Cache is the memory buffer on the drive, typically 64MB to 512MB. It smooths bursts of writing, though it cannot make the platters faster.

Workload rating is how much reading and writing per year the maker designs the drive for, from about 55TB a year on a desktop drive to 550TB on an enterprise one. A desktop PC rarely comes close to the low figure, so this matters mainly for a NAS or a drive that records continuously.

How the Value Ranking Works

We score each drive out of 100 from what its maker publishes and what Backblaze measures: recording type, workload rating, warranty, failure rate where the model is covered, spindle speed, MTBF and cache. Hard drives are scored only against other hard drives, so a hard drive’s 80 and an SSD’s 80 are not the same thing.

Value weighs that score against the price per terabyte of other hard drives the same size. At a typical price, value equals the score. Cheaper raises it and dearer lowers it, but price counts for less than quality.

A spec we hold no figure for scores zero rather than being skipped, so a drive nobody documents cannot outrank a fully specified one. The bar beside each score shows how much we could verify, and a low score on a low bar means undocumented rather than bad.

Failure Rates You Can Check

Backblaze runs tens of thousands of drives in its datacenter and publishes how often each exact model fails. Where a drive we list is in that fleet, and the sample is large enough to mean something, we show the rate and link the source. Most consumer drives are not covered, because the fleet is enterprise-heavy, and a drive without a published rate is not a worse drive.

Treat those numbers as a datacenter measurement: drives running continuously, in racks, under heavier use than a desktop. MTBF figures, by contrast, are the maker’s own design estimate rather than a measurement, which is why they carry little weight in the score.

Choosing a Size

Price per terabyte falls as drives get larger, so the biggest drive you can justify is usually the cheapest space. Weigh that against having your data on fewer drives: one 20TB drive failing loses more than one 8TB drive failing, and a hard drive is not a backup by itself. Sort by price per terabyte to see which sizes are genuinely good value today rather than merely cheap.