Storage
What is IOPS?
IOPS measures how many individual read or write operations a storage device completes per second. Random 4K IOPS at a queue depth of one is the number that predicts database behaviour; sequential throughput is the number that appears in marketing.
Why IOPS matters
Random 4K IOPS at a queue depth of one is the number that predicts database behaviour; sequential throughput is the number that appears in marketing.
IOPS in practice
When you are actually running a server, IOPS is what you watch when queries slow down. You look at your database's random 4K read latency and see if the disk is the bottleneck. If it is, you move to NVMe or add more drives. Ignore it and your application crawls under load, and every slow query costs you users. You can change your storage configuration, but it is not instant: moving a tier down requires a rebuild, and extra NVMe attaches as a second block device. Getting it wrong means your server feels fast in tests but falls over in production.
What people get wrong about IOPS
The misconception is that IOPS is a fixed number. It is not; it depends on queue depth and block size. A drive can claim high IOPS at high queue depths, but what matters for databases is random 4K at a queue depth of one. The correction: if you compare storage on marketing numbers, you will pick the wrong device. Look at the queue-depth-one figure.
IOPS — common questions
What queue depth should I use for IOPS testing?
For database workloads, use a queue depth of one. That is the number that predicts real behaviour because most OLTP queries issue single, independent reads. Higher queue depths can inflate IOPS numbers but do not reflect how your database actually hits the disk.
How does IOPS differ from throughput?
IOPS counts individual operations per second; throughput measures bytes per second. A sequential transfer like a backup might achieve high throughput but low IOPS, while a database does many small random reads, so IOPS matters more. Marketing often quotes the sequential number.
Where IOPS comes up
- How much faster is NVMe than SATA SSD? Roughly five times the random IOPS — about 500,000 versus 90,000 — and around five times lower latency, under 0.1 ms versus about 0.5 ms. Sequential throug…
- NVMe vs SSD vs HDD for a VPS NVMe reaches roughly 500,000 random IOPS with sub-100-microsecond latency; a SATA SSD manages around 90,000 IOPS; a 7,200 RPM HDD manages about 150. For an…
- How do I benchmark a VPS? Measure the three things that actually vary: single-thread CPU with sysbench, disk with fio at 4K random read/write, and network with iperf3 to a known end…
More from storage
- NVMe
- NVMe is a storage protocol that connects solid-state drives directly over PCIe, reaching roughly 500,000 random IOPS with sub-100-microsecond latency.
- RAID 10
- RAID 10 mirrors data across pairs of drives and stripes across the mirrors, giving both redundancy and high performance at the cost of half the raw capacity.
- Snapshot
- A snapshot is a point-in-time copy of a virtual machine disk, taken instantly and stored on the same infrastructure.