Which of the EBS volume types can be used as boot volumes when you create EC2 instances?
Only SSD-backed EBS volume types — gp2, gp3, io1, and io2 — can be used as boot (root) volumes for EC2 instances. The HDD-backed volume types (st1 and sc1) cannot be used as boot volumes because their performance characteristics are not suitable for OS boot operations.
Booting an operating system requires fast random I/O — reading small, scattered blocks of data quickly during the kernel and service startup process. SSD-based volumes excel at this because they are optimized for IOPS (Input/Output Operations Per Second). HDD-based volumes (st1 and sc1) are designed for sequential, throughput-heavy workloads and perform poorly on the random small-block reads that OS booting requires. AWS therefore restricts boot volumes to SSD types only.
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gp2 (General Purpose SSD v2) — Supported. Was the previous default boot volume type. Being replaced by gp3.
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gp3 (General Purpose SSD v3) — Supported and RECOMMENDED. Current default boot volume type. 20% cheaper than gp2 with better baseline performance.
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io1 (Provisioned IOPS SSD v1) — Supported. Used for boot volumes when consistent, high IOPS is required for the OS disk (rare, but supported for demanding applications).
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io2 (Provisioned IOPS SSD v2) — Supported. Most durable SSD option, used in mission-critical environments needing high IOPS on the OS volume.
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st1 (Throughput Optimized HDD) — NOT supported as a boot volume. Designed for large sequential reads (Hadoop, log processing). Cannot boot from st1.
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sc1 (Cold HDD) — NOT supported as a boot volume. Designed for infrequently accessed cold storage. Absolutely not suitable for OS boot operations.
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Instance Store — Not an EBS volume, but technically can be used as a boot volume on specific instance types. Data is lost on stop/terminate.
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gp3 — Use for most workloads: web servers, app servers, general-purpose instances, development environments. Best cost-performance ratio.
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io1/io2 — Use when the OS disk itself requires very high IOPS — for example, databases that do intensive random reads/writes on the OS partition, or systems with demanding startup sequences.
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gp2 — Avoid for new instances. AWS recommends migrating existing gp2 boot volumes to gp3 for cost savings.
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General rule — 99% of EC2 instances should use gp3 as the boot volume type.