> ## Documentation Index
> Fetch the complete documentation index at: https://docs.murmur.dev/llms.txt
> Use this file to discover all available pages before exploring further.

# Agent disk sizing and storage cost

> How agent VM boot disks are sized and grow automatically, and how disk type and size drive your storage cost.

Agent VMs start with a small boot disk and **grow it automatically** when it fills up. You pay for the size an agent has grown into, for the hours it is that size — not a large fixed disk from the moment it starts.

## How it works

Every agent runs on a VM with a single boot disk. The disk is created at a small **floor** size. While the agent works, Murmur watches how full the disk is; when it crosses a high-usage mark, Murmur grows the disk — online, without interrupting the agent — to the next size up. Growth is geometric (each step multiplies the size), up to a **ceiling** you configure, so a busy agent reaches the space it needs in a few steps and a light agent never grows at all. This works the same on GCP and AWS: both grow the disk in place while the agent runs.

You do not need to do anything for this to happen. It is automatic.

## Storage types

An [environment](/catalog/environment)'s disk type sets both performance and price. The built-in types:

| Storage type | Catalog disk type | Performance | Relative cost |
| - | - | - | - |
| Standard | `murmur-pd-balanced` | General-purpose SSD; speed scales with size | Standard |
| Fast | `murmur-pd-ssd` | Faster SSD; speed scales with size | Higher |
| Economy | `murmur-pd-standard` | HDD; lowest speed | Lowest |
| Guaranteed-IOPS | `murmur-hyperdisk-balanced` | SSD with fixed high IOPS, independent of size | Standard+ |

For Standard, Fast, and Economy, a smaller disk is also a slower disk — performance scales with size. If your agents do heavy I/O (large dependency installs, container builds), either set a larger floor or choose Guaranteed-IOPS, whose performance does not depend on size.

See the [disk-type reference](/catalog/disk-type) for the full field list, and [Pricing](/pricing#disk-type-rates) for current rates.

## Configuring the floor, ceiling, and type

Disk sizing lives on the [environment](/catalog/environment) your workspace's placement uses:

* `disk_type_ref` — the storage type (one of the types above).
* `disk_size_gb` — the **floor**: the size every VM starts at. Defaults to 10 GiB.
* `disk_max_size_gb` — the **ceiling**: the largest size the disk auto-expands to. Left at `0`, the default ceiling applies — 200 GiB, or your floor if the floor is larger — so **auto-expand is on by default** and you do not have to set anything for a disk to grow. A floor already above 200 GiB simply stays a fixed-size disk at the floor (there is nothing to grow into).

Set these on the environment with [`murmur set environment`](/cli/set) and set the workspace's `environment_ref` to this environment. This is the single place disk sizing is configured — there is no per-spawn override.

<Note>
  To pin every VM to one fixed size that never grows, set `disk_max_size_gb` **equal to** `disk_size_gb`. The disk is created at that size and the floor and ceiling coincide, so there is nothing to grow into. A ceiling below the floor is rejected when you save the environment.
</Note>

## Seeing the cost

Each agent has a **Cost** page showing the storage type and current size its VM is using right now, alongside what the agent has been charged. You pay for the size the disk has grown into, for the hours it is that size. See [Pricing](/pricing#disk-type-rates) for the storage rates.


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