20TB NAS Hard Drives - Live Prices

What 20TB costs in a NAS today

We can currently price 5 in-stock 20TB NAS drives from 2 brands (Seagate and WD). The best rate is $36.00 per terabyte, against a $40.00 median across the same capacity - a spread worth noticing, because at this size the gap between the cheapest listing and the middle of the market is real money rather than rounding. The lowest ticket price on a single drive is $720.

The listings split 3 new and 2 recertified, and for a NAS that distinction carries more weight than it does in a desktop. An array runs its drives continuously, so the warranty behind each one is a live concern rather than a formality - new carries the manufacturer's, recertified carries a reseller's, and the discount is the compensation for that difference. Our recertified guidance covers what to check before a drive goes into a pool.

What 20TB drives actually build

A NAS buyer is choosing a configuration rather than a drive, and the number that decides it is usable capacity after parity. At 20TB per drive that works out as follows, before filesystem overhead and before you leave the headroom a pool needs to stay healthy:

Those totals are drives only. The enclosure, the memory and the drive bays you leave empty for a future expansion are separate costs, and the last of those is the one people forget: filling every bay on day one means the next upgrade is a full replacement rather than an addition. Our RAID planner works through the configurations properly, and replacing drives with larger ones covers the upgrade path when you get there.

Recording technology at this capacity

All 5 in-stock 20TB drives we can verify use conventional recording, which is what an array needs. Shingled drives overlap their tracks to gain density, and the cost of that is rewrite behaviour that can turn a RAID rebuild into a multi-day event or make it fail outright. At this capacity the stock we track is clean.

Warranty terms in stock run 5 years, and workload ratings run 300 to 550TB per year. That rating is the manufacturer's statement about sustained annual writes, and a NAS serving a household rarely approaches it - it matters when the array is a backup target or a surveillance recorder rather than a media library.

Is 20TB the right rung?

At 20TB the rebuild window is the constraint worth planning around. Resilvering a drive this size takes many hours and often more than a day depending on how busy the pool is, and for the whole of that window a single-parity array has no redundancy left. That is the argument for RAID 6 or RAIDZ2 at this capacity rather than RAID 5, and it is an argument about time exposed rather than about any particular drive being unreliable.

The general rule is that cost per terabyte improves as you go up the ladder until it does not, and where it stops improving moves with the market rather than sitting at a fixed capacity. Comparing the live rate on this page against the neighbouring rungs is the only reliable way to find that point on the day you are buying.