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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.

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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.

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Storage types

An environment’s disk type sets both performance and price. The built-in types: 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 for the full field list, and Pricing for current rates.

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Configuring the floor, ceiling, and type

Disk sizing lives on the 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 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.
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.

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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 for the storage rates.