Premium SSD vs Standard SSD on Azure: what you pay for

Picture a 512 GiB data disk behind a web server, holding 100 GiB. As a P20 or an E20, you pay for all 512 GiB.

The E20’s tier costs $34.82 a month less. But its transaction charges overtake that gap once the disk averages more than about 66 transactions a second.

Both types charge by size tier

Premium SSD runs from P1 to P80, and Standard SSD from E1 to E80. Each size tier is a fixed size between 4 GiB and 32,767 GiB.

Azure rounds the size you provision up to the next tier and charges for that tier, prorated by the hour. So a 200 GiB Standard SSD is charged as an E15, the 256 GiB tier. Microsoft’s pricing page adds that the rate is the same however much of the disk you use.

Standard SSD also charges per transaction

Microsoft’s guide to disk charges is direct about Premium SSD: “Unless you enable on-demand bursting, there are no transaction costs for Premium SSD.”

Standard SSD charges for transactions, and any operation counts: reads, writes and deletes. Each I/O of up to 256 KiB counts once, and a larger one counts as several.

In East US the rate is $0.002 per 10,000 transactions on locally redundant storage (LRS). Each tier caps the paid transactions per hour. Anything above the cap in that hour costs nothing.

East US prices, tier by tier

The table gives East US pay-as-you-go prices for Premium SSD LRS vs Standard SSD LRS, the SKUs Premium_LRS and StandardSSD_LRS. Prices are from Microsoft’s managed disks pricing page in October 2026. Performance is what Microsoft publishes for each tier.

At these sizes Standard SSD lists at 49% to 59% of the Premium SSD price, before transactions. The last column is a disk at its hourly cap for every hour of a 730-hour month.

Zone-redundant storage (ZRS) costs more. A P20 ZRS lists at $109.81 and an E20 ZRS at $57.60, 1.5 times their LRS prices. Azure disk LRS vs ZRS covers the difference.

Prices differ by region and change over time, so check yours on the managed disks pricing page. The Azure disk pricing calculator shows what a disk costs a month at list price.

Premium SSD buys provisioned performance. Microsoft guarantees a Premium SSD’s capacity, IOPS and throughput once it’s provisioned. It designs the disk to deliver single-digit millisecond latency and those targets 99.9% of the time.

Standard SSD also targets single-digit milliseconds. But its IOPS and throughput are ceilings, met 99% of the time. Microsoft says actual figures can vary with traffic patterns.

The Azure Standard SSD vs Premium SSD IOPS gap opens with size. At 128 GiB the two match on paper, but above it Premium SSD climbs with size.

Every Standard SSD from E1 to E50 (up to 4,096 GiB) stays at up to 500 IOPS and 100 MB/s. A P30 gives ten times the IOPS of an E30 of the same size.

Small disks, bursts and performance tiers

Standard SSD’s base IOPS pass 500 only at E60, the 8,192 GiB tier, with up to 2,000. Performance plus, where enabled, takes an E30 to up to 1,500.

Both types can burst for short peaks, for up to 30 minutes. Premium SSD P20 and smaller can burst to 3,500 IOPS and 170 MB/s. Standard SSD bursts to 600 IOPS and 150 MB/s on E20 and smaller, and to 1,000 IOPS and 250 MB/s on an E30.

From P30 up, Premium SSD bursts only with on-demand bursting. You enable it and pay for it, with an hourly fee plus burst transactions.

Some Premium SSD sizes can select a higher performance tier without growing, and you pay for that tier until you change it back. A Standard SSD’s tier is set by its size. Azure disk performance tiers covers when that’s worth it.

Limits outside the disk

A Premium SSD needs a VM size that supports Premium storage, while Standard SSD is available on all Azure VMs. The VM size also has its own IOPS and throughput caps, which Azure disk IOPS vs throughput explains.

A third option drops the tiers. Premium SSD v2 charges for each GiB, plus IOPS above 3,000 and throughput above 125 MB/s. Premium SSD v2 vs Premium SSD works through its prices.

At $0.002 per 10,000 transactions, that pays for about 238,000 transactions an hour. That’s around 66 a second (238,000 ÷ 3,600). Average more than that over the month, and the E20 costs more than the P20.

The E20 also gives less than a quarter of the P20’s IOPS. At its cap of 502,000 paid transactions an hour, the E20’s transactions come to $73.29 a month. So it costs $38.40 + $73.29 = $111.69, which is $38.47 more than the P20.

The break-even at other sizes

An E10 costs more than a P10 above about 69,000 transactions an hour (19 a second). An E30 costs more than a P30 above about 400,000 an hour (111 a second).

At every size in the table above, a Standard SSD at its cap costs more than the Premium SSD of the same size.

How to count a disk’s transactions

In your Azure charges, Standard SSD transactions appear on a Disk Operations meter beside the disk’s tier meter.

For a disk that’s still Premium SSD, use the VM’s metrics in the Azure portal. Data Disk Read Operations/Sec and Data Disk Write Operations/Sec, split by LUN, show how busy each data disk is.

Treat that as an estimate. The read metric includes reads served from host cache when read-only or read/write caching is on. And an I/O over 256 KiB counts as several transactions.

Standard HDD is the third type charged by size tier. It runs from S4 to S80, starting at 32 GiB, with up to 500 IOPS and 60 MB/s through S50.

An S20 (512 GiB) lists at $21.76 a month in East US. It charges for transactions too, counted in 16 KiB units and capped per disk per hour.

Microsoft designs Standard HDD for write latency under 10 ms and read latency under 20 ms, for most operations. It says Standard HDD doesn’t suit OS disks or transactional databases. On September 8, 2028, Microsoft retires the use of Standard HDD as an OS disk.

Microsoft’s high availability guide says which VMs get the highest single-VM uptime service level agreement (SLA). Their OS disk is Premium SSD, and their data disks are all Premium SSD, Premium SSD v2 or Ultra Disk.

Pick by the I/O you’ve measured on the disk:

• Standard SSD: a disk within 500 IOPS and 100 MB/s and well under its transaction break-even, such as a web server or test VM.
• Premium SSD: production workloads, and any single VM that needs the top SLA. It also suits a disk of 4 TiB or less that needs more than 500 IOPS for longer than a burst. On a Standard SSD from E30 up, performance plus can lift that limit.
• Standard HDD: backups and large sequential files.

Switching between Premium SSD, Standard SSD and Standard HDD updates the disk’s SKU, and the conversion itself is instantaneous. But Microsoft’s conversion guide says it requires a restart of the VM, so schedule it in a maintenance window. You can change a disk’s type twice per day.

Going from Premium to Standard needs no VM resize. Coming back needs a VM size that supports Premium storage.

The size doesn’t change, so a half-empty P30 becomes a half-empty E30. Disk reservations exist only for Premium SSD SKUs from P30 to P80. Each is bought for one SKU in one region, so a reservation won’t cover the converted disk.

These Azure CLI commands from Microsoft’s guide convert one data disk:

1. Look up the VM the disk is attached to and store its ID.

   $ vmId=$(az disk show --name <disk-name> --resource-group <resource-group> --query managedBy --output tsv)

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2. Deallocate the VM. This stops it, so every service on it is down until step 4. Microsoft says the VM’s temporary disk isn’t persisted in Azure Storage, so keep nothing there that you need.

   $ az vm deallocate --ids $vmId

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3. Change the disk’s SKU. Use StandardSSD_ZRS instead to keep a zone-redundant disk zone-redundant.

   $ az disk update --sku StandardSSD_LRS --name <disk-name> --resource-group <resource-group>

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4. Start the VM.

   $ az vm start --ids $vmId

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Disk type sets the price of each tier, and the tier sets how much space you pay for. Azure can grow a managed disk but not shrink it, as Can you shrink an Azure managed disk? explains.

Amoeba optimizes block storage on Azure and AWS by working on the size. It moves a VM’s data disks onto one btrfs pool sized to your data, with room to grow. It works on running Windows and Linux VMs, and never touches the OS disk.

• The move. Amoeba copies your data while your services run. Then it switches each mount to the pool, with a short restart of the services that use it.
• Rightsizing. It grows the pool before it fills, and sooner when data arrives fast. When your data goes down and stays down, it shrinks the pool one disk at a time.

The pool’s disk type

The pool uses Premium SSD v2 where your VM’s region and zone offer it, and Premium SSD otherwise. Its disks are always locally redundant, so data on a ZRS disk loses its zone redundancy.

Neither pool type carries Standard SSD’s per-transaction meter. Data on Standard SSD or Standard HDD moves to one of those two types, at a higher rate per GiB in East US. So the saving there comes from the smaller size.

On Azure, Amoeba prices disks from the Azure Retail Prices API. The free block storage assessment writes one PDF and sends nothing to Zoorik. Amoeba is in early access.

Azure managed disk cost optimization covers Amoeba on Azure in full.