Data center hard drives: large capacities, fleet arithmetic and failure ratings

Large-capacity data centre hard drives on Amazon.co.uk

Four sizes get their own tables, new drives only: 26 TB, 24 TB, 22 TB and 20 TB, drawn from the Exos, Ultrastar, Toshiba MG and WD Gold lines. The largest with a table here is 26 TB. That is a choice about what we table, not a statement that nothing bigger is on sale. Seagate's latest Exos drives come in 24 TB to 32 TB options, but that describes the maker's range, and only a row below shows a listing we can price.

• 26 TB: 2 in stock, lowest £599.00, or £23.04/TB
• 24 TB: 2 in stock, lowest £1,059.91, or £44.16/TB
• 22 TB: 5 in stock, lowest £800.00, or £36.36/TB
• 20 TB: 3 in stock, lowest £889.23, or £44.46/TB

A table at one size can hold few rows, and can change or empty between visits. One rate cuts across them all: the lowest price per TB among the 84 new drives on these lines is £23.04/TB, on Seagate Exos 26TB Internal Hard Drive at £599.00. This shorter table shows 12 of them, and its best rows need not be large drives, since it is not limited by size.

Fleet arithmetic: how many drives for a target capacity

The first sum is division, rounded up, because nobody buys a fraction of a drive. Capacity here is raw and decimal, before any redundancy: Seagate's data sheet states that one terabyte equals one trillion bytes.

The gap between the rows is bays. Moving from 20 TB to 26 TB drives saves 11 bays per 1,000 TB. Whether that is worth paying for depends on your chassis, and on your own power and cooling figures. We do no energy sums on this page.

To cost a build, multiply one row's price by the drive count. At 24 TB the lowest listing is £1,059.91, so 42 drives come to 42 times that figure. We do not print the total, because the table prices one listing and cannot show that 42 units are available at that price. Confirm quantity and any per-customer limit on Amazon.co.uk. For a fleet, treat the price per TB as the opening comparison and that quantity check as the one that settles it.

From raw to usable capacity

Redundancy changes the count. The calculator below opens on 12 drives of 24 TB in RAID 6: 288 TB raw and 240 TB usable after double parity. Reaching 1,000 TB usable with groups of that shape takes 5 groups, or 60 drives, and yields 1,200 TB. The 42 drives in the table above would not do it. Change the inputs to match your own layout.

Workload arithmetic: what 550 TB a year comes to

Two makers we read state the same workload figure: Toshiba rates its MG series for 24/7 operation at 550 TB/year, and WD rates the Ultrastar DC HC590 for 550TB/year workloads. We hold no workload figure for Exos or WD Gold. Divided by 365, 550 TB is about 1.5 TB a day per drive. Over the 5-year warranty each maker states for those ranges, it comes to 2,750 TB. On a 24 TB drive, 550 TB is about 23 times the drive's own capacity each year.

Toshiba's page gives no split, so we cannot say how reads count; counting all traffic is the cautious reading, and that is our suggestion, not Toshiba's.

Data center hard drive failure rate: maker ratings, not fleet results

The figures we can print are ratings. Seagate gives its 32 TB, 30 TB, 28 TB and 24 TB Exos models a reliability rating of 0.35% AFR at full 24x7 operation. WD lists the Ultrastar DC HC590 at 0.35% annualised failure rate too, and marks it as a projected value. Neither is a measurement of drives bought from a table on this page.

Set against a fleet, 0.35% of 42 drives is about 0.15 failures a year on paper, which is less a forecast than a sign of how little a small fleet can test. A single real failure among 42 is one drive in 42, so one event moves any rate you work out a long way. A year of watching those drives yields 15,330 drive-days. Plan spares from your own tolerance for downtime.

Backblaze publishes failure statistics from the drives in its own data centres, built from a snapshot of each operational drive taken every day. We quote no fleet rate from it, so go to Backblaze's own Drive Stats for those numbers. Its caution is the part to keep: even drive models from the same maker have variable reliability, so a brand's rate does not predict one model, let alone one drive.

Do data centers use SSD or HDD? The one fleet we can show

We can show only one fleet using both: Backblaze's statistics cover the hard disk drives and the solid state drives in its data centres. We have not found a document for this page that gives an industry split or a cost comparison, so we will not state which is winning, or by how much.

The tables here are hard drives only. Enterprise SSD listings are priced separately, and SAS vs NVMe deals with the interface difference.

Seagate data center hard drive, Toshiba datacenter HDD, WD: what makers state

These are not like-for-like rows, since each maker chooses what its page or sheet leads with. A point on one line only means that we read it in that maker's document, and nothing about the others. The ranges are split out at Seagate Exos, WD Ultrastar and Toshiba MG series.

These tables are new drives only. If a fleet budget points you towards used stock, note that Seagate's recertified drives are backed by a six-month warranty, and weigh refurbished enterprise hard drives on that basis.