Persistent Disk Calculator
Size a Persistent Disk and see the IOPS and throughput its capacity earns before the instance vCPU limit clips it.
Inputs
Per-instance disk limits step up with vCPU count, so a small VM cannot use a large disk's full rating.
Read IOPS per Disk
3,000IOPS
Write IOPS per Disk
3,000IOPS
Read Throughput per Disk
140MiB/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
Values used
Provisioned size per disk = 500 GB; Number of disks = 2 disks; Disk type = pd-balanced (general-purpose SSD); vCPUs on the attached instance = 8 vCPU; pd-standard price per GB = 0.0400 USD/GB-month; pd-balanced price per GB = 0.1000 USD/GB-month; pd-ssd price per GB = 0.1700 USD/GB-month; pd-extreme price per GB = 0.1250 USD/GB-month; pd-extreme provisioned IOPS = 30,000 IOPS; pd-extreme price per provisioned IOPS = 0.0650 USD/IOPS-month; Snapshot data stored = 300 GB; Snapshot price per GB = 0.0260 USD/GB-month
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.
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
How it works
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
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.