We are currently using an HDD for our NetApp storage for our VMs. We're considering replacing them with SSDs, but many disk manufacturers have different performance. What range of latencies can we expect from SSDs versus HDDs? How much better are SSDs on average?
['https://superuser.com/questions/1414662', 'https://superuser.com', 'https://superuser.com/users/639471/']
The latencies of an SSD vary hugely, but in terms of IOPs (which us probably the term you want to google)you are looking at an increase in the order of 2-5 magnitudes. (Ie 100 iops for HDD, starting at more then 10000 + for an SSD).

Have a look at <https://en.m.wikipedia.org/wiki/IOPS>

SSDs are like a night and day difference. I would only use hdds for backups and unimportant archival data - like videos, music collections. A heavily swapping HDD can render a system unuseable - while it will just be a bit sluggish on SSD.

Speedwise SSDs are at least 5 times as fast in sequential reads and writes - which represents the closest benchmark

You did not ask, but SSD is also over 5 times as reliable as hdd (but unlike hdd more likely to fail completely and without warning - so RAID is still important)
NVMe SSD latencies can be as low as [250 µs](https://phoenixnap.com/kb/nvme-vs-sata-vs-m-2-comparison) (microseconds). Much faster than the typical [2-4 ms](https://en.wikipedia.org/wiki/Hard_disk_drive_performance_characteristics#Rotational_latency) (millisecond) latencies of HDDs that spin at 7,500 - 15,000 RPM.

0.25 ms vs. 2 ms means that an NVMe SSD will have about 1/8th the latency of a fast 15,000 RPM HDD.

However a lot of factors can affect both of these numbers. It is possible for overly-taxed SSDs to provide >1 millisecond performance, and a cache on an HDD could at times provide zippier data access to commonly-used blocks. YMMV and you should consider running your own tests for the disks you are considering deploying.