Managed Disks
How managed disk recommendations work, the four ways a disk can get cheaper, the disk toggles and the disk card. Select a disk on the Recommendations Page to open its card.
8 Sections
Disks never shrink
Azure doesn't support shrinking a managed disk. Recommendations change only the performance tier or SKU; the provisioned size stays the same and sets the floor for every target.
What's Analyzed
Attached managed disks on Premium SSD or Standard SSD, LRS or ZRS, including disks attached to deallocated VMs. Sizing uses per-disk Azure Monitor metrics (Composite Disk Read/Write Operations/sec and Read/Write Bytes/sec), because VM-level disk percentages can't size an individual disk.
Standard HDD disks, Premium SSD v2 and Ultra Disks aren't analyzed as sources. Unattached disks are in Orphaned Resources.
On first collection, StratoLens loads the history Azure Monitor still holds (about 93 days), so most disks have enough data on the first scan after metrics collection starts.
The Four Levers
Each scan stores one alternative per lever. The disk toggles decide which levers are eligible, and the card shows the cheapest eligible one.
Tier Downgrade
Lowers a Premium SSD's performance tier online, with no VM downtime. Can't go below the tier that matches the disk's size, and downgrades are allowed once per 12 hours. Shared disks need all attached VMs stopped. Always eligible.
SKU Conversion
Converts to Standard SSD. Requires the attached VM deallocated, and conversions are limited to twice per day. Eligible when Allow Changes Requiring VM Stop is on, or the VM is already stopped.
HDD Conversion
Converts to Standard HDD, with the same deallocation rule. Never offered for ZRS disks. Always eligible for disks on stopped VMs; for running VMs, only when Allow Changes Requiring VM Stop and Allow Standard HDD Targets are both on.
v2 Migration
Migrates to Premium SSD v2 with provisioned IOPS and throughput. Data disks only: Premium SSD LRS, host caching None, not shared, with Premium SSD v2 priced in the region. Eligible only when Allow Premium SSD v2 Migration (One-Way) is on.
SKU conversions need downtime
Converting to Standard SSD or Standard HDD requires the attached VM to be deallocated. Plan downtime, or turn off Allow Changes Requiring VM Stop to see only online changes.
Premium SSD v2 migration is one-way
There is no direct conversion back to Premium SSD v1. See the prerequisites before migrating.
Fit Rule
A target fits when both P95 IOPS and P95 throughput stay within the aggressiveness ceiling of the target's limits.
- Peaks above the target's base performance but within its credit-burst limit keep the target, with the warning "Observed peaks exceed the target base performance but are covered by credit bursting." Peaks above the burst limit reject it.
- Premium SSD v2 targets are provisioned from P95 demand plus headroom, never below the free baseline of 3,000 IOPS and 125 MB/s.
- Standard SSD and Standard HDD bill per 10,000 operations; Premium SSD doesn't. Savings for Standard targets subtract an estimated transaction cost based on observed operations, so high-I/O disks don't show overstated savings. When a region has no transaction price, that target is skipped.
Disks on Stopped VMs
A disk attached to a deallocated VM has no I/O demand, so the fit check is skipped and conversions need no extra downtime. These get the Stopped VM recommendation type.
The deallocation duration is measured from the VM's last metric date, and deallocated days count as data days for the Managed Disks Minimum Data Window. That window is the only age gate, so review the "stopped since" date on the card before converting.
Zero-disruption changes
Disks on VMs that are already stopped can be converted with no additional disruption.
Disk Toggles
These three toggles live in the Managed Disks section of Toggle Options.
- Allow Changes Requiring VM Stop
- Default on. Includes SKU conversions, which need the attached VM deallocated. Turn off to see only online changes. Disks on already-stopped VMs are always shown.
- Allow Standard HDD Targets
- Default off. Includes Standard HDD conversions for disks on running VMs. Needs Allow Changes Requiring VM Stop on. Disks on stopped VMs always show HDD targets.
- Allow Premium SSD v2 Migration (One-Way)
- Default off. Includes Premium SSD v2 migrations for eligible data disks. Opt-in even for disks on stopped VMs.
Reading the Disk Card
The card title follows the chosen lever: Performance Tier Downgrade, Disk SKU Conversion, Stopped VM Disk Conversion or Premium SSD v2 Migration Recommendation. Alongside the badges, rationale and estimated savings described in How Sizing Works, it shows:
- Slot badge
- The lever behind the pick: Tier Downgrade, SKU Conversion, HDD Conversion or v2 Migration.
- Current and Recommended
- SKU and tier, provisioned IOPS and MB/s, and monthly cost. The size line confirms the size never changes and marks OS disks.
- Disruption banner
- Green when the VM is already stopped. Amber when the change requires a VM stop or is a one-way migration, with any prerequisites and lever warnings.
- Estimated Savings
- For Standard targets, includes the estimated transaction cost per month.
- Utilization Evidence
- IOPS and throughput: P95 Avg, P95 Peak, Maximum and Provisioned. For disks on stopped VMs, the deallocation duration and stop date instead.
- Confidence Analysis
- The three shared factors. Disks on stopped VMs show a single VM Deallocation Duration factor.
The panel header has View in Explorer only; there is no View Performance button for disks.
Premium SSD v2 Prerequisites
A Premium SSD v2 Migration card lists these before you act:
- Disable on-demand bursting first, when bursting is on.
- Verify there's no double encryption, Azure Site Recovery is disabled, Azure Backup uses an Enhanced policy, and the logical sector size is 512 bytes. StratoLens can't check these from inventory.
- Expect degraded performance while the conversion runs. Going back to Premium SSD v1 is possible only through snapshot migration.
Troubleshooting
A Premium disk has no recommendation
Answer
No cheaper tier or SKU fits its P95 IOPS and throughput at the current aggressiveness, or the disk's size already sets the lowest tier. Check the Minimum Savings threshold too.
I only want changes I can make without downtime
Answer
Turn off Allow Changes Requiring VM Stop. Only performance tier downgrades remain, plus disks on already-stopped VMs.
I don't see Standard HDD options
Answer
Turn on Allow Standard HDD Targets, with Allow Changes Requiring VM Stop on. HDD is never offered for ZRS disks.
I don't see Premium SSD v2 options
Answer
Turn on Allow Premium SSD v2 Migration (One-Way). Only eligible data disks in regions with Premium SSD v2 pricing get this option.
A stopped VM's disk shows a recommendation after only a few days
Answer
Deallocated days count toward the minimum data window. Raise the Managed Disks Minimum Data Window in Settings > Scanner if you want to wait longer.