Disk Tier Downgrade (Azure)
CostLens flags attached Premium SSD disks with sustained low throughput that could move to Standard SSD for the same capacity at a lower rate.
CostLens flags attached Premium SSD disks with sustained low throughput. Premium SSD is priced for high, consistent IOPS — a disk that reads and writes very little is paying for performance it never uses. Moving it to Standard SSD keeps the same capacity at a much lower per-GB rate.
Applied with a brief detach/retype
Changing a disk's account type is done in Azure (or via CostLens once write access is granted). It's reversible, but changing the type of an OS disk needs the VM stopped — schedule it in a maintenance window.
How it works
Disks are enumerated
CostLens lists managed disks via the Azure Resource Manager API and keeps the Premium SSD, currently-attached ones.
Throughput is measured
The disk's Composite Disk Read/Write Bytes/sec metrics are read over 14 days. Disks below ~50 KB/s average are treated as low-throughput.
Savings are computed
Priced as disk size × (Premium per-GB rate − Standard SSD per-GB rate).
What to do
- Confirm the disk doesn't need Premium's latency/IOPS guarantees for occasional bursts (databases, latency-sensitive apps).
- Change the disk to Standard SSD (disk → Configuration → Account type). Stop the VM first if it's an OS disk.
Severity levels
| Severity | Estimated monthly savings |
|---|---|
| critical | >$500 |
| high | $100–$500 |
| medium | $20–$100 |
| low | <$20 |
Required permissions
- Detect:
Reader(disk metadata + Monitor metrics) — see Azure Accounts.
Limitations
- Throughput alone can miss latency-sensitivity — a disk with low average throughput but strict latency needs may still warrant Premium. Review before converting.
- Unattached Premium disks are covered by Unattached Managed Disk, not here.
- Disks with no metric data available are skipped rather than guessed.