Persistent Disk Calculator
Size a Persistent Disk and see the IOPS and throughput its capacity earns before the instance vCPU limit clips it.
About Persistent Disk Calculator
On pd-standard, pd-balanced and pd-ssd you do not buy IOPS, you buy GB and the IOPS come with them at a fixed rate per GB. The instance then applies its own ceiling, which steps up with vCPU count, so a 4-vCPU VM cannot use anything like the rating of a multi-terabyte pd-ssd volume. Undersized disks throttle databases in a way that looks like an application problem, and oversized ones bill for IOPS the VM can never issue — the two limits have to be sized together. Verify the per-GB prices for your region in the Google Cloud pricing calculator, since disk rates differ noticeably between regions.
Formula
Persistent Disk
read IOPS = min(GB × IOPS-per-GB for the type, the per-instance ceiling for that vCPU count); cost = GB × type price × disks + snapshot GB × snapshot price.
- IOPS-per-GB
- 6 for pd-balanced, 30 for pd-ssd, 0.75 read and 1.5 write for pd-standard
- per-instance ceiling
- Disk limit that steps up with the vCPU count of the attached VM
- pd-extreme
- The one type where IOPS are provisioned and billed separately from capacity
Worked example
With the default values below, Persistent Disk Calculator returns Read IOPS per Disk of 3,000. Change any input above and every figure here is recalculated in your browser.
Inputs used
- Provisioned size per diskaccepts 10–65,536 GB
- 500 GB
- Number of disksaccepts 1–128 disks
- 2 disks
- Disk typeone of pd-standard (HDD), pd-balanced (general-purpose SSD), pd-ssd (performance SSD), pd-extreme (provisioned IOPS)
- pd-balanced (general-purpose SSD)
- vCPUs on the attached instanceaccepts 1–416 vCPU
- 8 vCPU
- pd-standard price per GBaccepts 0–5 USD/GB-month
- 0.04 USD/GB-month
- pd-balanced price per GBaccepts 0–5 USD/GB-month
- 0.1 USD/GB-month
- pd-ssd price per GBaccepts 0–5 USD/GB-month
- 0.17 USD/GB-month
- pd-extreme price per GBaccepts 0–5 USD/GB-month
- 0.125 USD/GB-month
- pd-extreme provisioned IOPSaccepts 0–120,000 IOPS
- 30,000 IOPS
- pd-extreme price per provisioned IOPSaccepts 0–5 USD/IOPS-month
- 0.065 USD/IOPS-month
- Snapshot data storedaccepts 0–200,000 GB
- 300 GB
- Snapshot price per GBaccepts 0–5 USD/GB-month
- 0.026 USD/GB-month
Results
- Read IOPS per Disk
- 3,000 IOPS
- Write IOPS per Disk
- 3,000 IOPS
- Read Throughput per Disk
- 140 MiB/s
- Performance Limited By
- Provisioned capacity — add GB to add IOPS
- Monthly Storage Cost
- $107.80
- Capacity Charge
- $100.00
- Snapshot Charge
- $7.80
- Cost per 1,000 Read IOPS
- $16.67
Step by step
- 1Values used
- 2Persistent Disk
- 3Read IOPS per Disk= 3,000 IOPS
- 4Write IOPS per Disk= 3,000 IOPS
- 5Read Throughput per Disk= 140 MiB/s
- 6Performance Limited By= Provisioned capacity — add GB to add IOPS
- 7Monthly Storage Cost= 107.80
- 8Capacity Charge= 100.00
Assumptions and limits
- The result is derived only from the 12 inputs listed above. Anything not among them is not part of the calculation.
- In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
- Figures are rounded for display to 2 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.
Frequently Asked Questions
How is Persistent Disk calculated?
read IOPS = min(GB × IOPS-per-GB for the type, the per-instance ceiling for that vCPU count); cost = GB × type price × disks + snapshot GB × snapshot price. On pd-standard, pd-balanced and pd-ssd you do not buy IOPS, you buy GB and the IOPS come with them at a fixed rate per GB. The instance then applies its own ceiling, which steps up with vCPU count, so a 4-vCPU VM cannot use anything like the rating of a multi-terabyte pd-ssd volume.
Why does Persistent Disk matter?
Undersized disks throttle databases in a way that looks like an application problem, and oversized ones bill for IOPS the VM can never issue — the two limits have to be sized together. Verify the per-GB prices for your region in the Google Cloud pricing calculator, since disk rates differ noticeably between regions.
What values do I need to enter?
This calculator takes 12 inputs: Provisioned size per disk, Number of disks, Disk type, vCPUs on the attached instance, pd-standard price per GB, pd-balanced price per GB, pd-ssd price per GB, pd-extreme price per GB, pd-extreme provisioned IOPS, pd-extreme price per provisioned IOPS, Snapshot data stored, Snapshot price per GB. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.
Why does adding vCPUs make my disk faster?
Because Persistent Disk performance is capped per instance as well as per disk. The instance ceiling rises in steps with vCPU count, so a larger machine shape unlocks more of the IOPS your disk size already entitles you to.