Update pool properties (e.g. autotrim) or add vdevs
AI agents use pool_update to create or update resources in Truenas — usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your Truenas environment.
This tool modifies TrueNAS storage pool configuration, which is a Write operation. While adding vdevs is a significant storage infrastructure change, it is reversible (vdevs can be removed or replaced). It does not delete data irreversibly (Destructive) nor triggers financial transactions (Financial).
From the tool's definition Tool name 'pool_update' and description 'Update pool properties (e.g. autotrim) or add vdevs' indicates reversible modification of storage pool configuration.
Documented attack patterns abuse exactly the kind of access pool_update gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and Truenas, and nothing reaches the server without passing your rules. This is the rule we recommend for pool_update:
{
"version": "1",
"default": "deny",
"tools": {
"pool_update": {
"limits": [
{
"counter": "pool_update_rate",
"window": "minute",
"max": 30,
"scope": "grant"
}
]
}
}
}pool_update stays usable, but capped — an agent stuck in a loop can't make hundreds of changes a minute. Everything else on the server is denied unless you say otherwise.
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Update pool properties (e.g. autotrim) or add vdevs. It is categorised as a Write tool in the Truenas MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.
Register the Truenas MCP server in PolicyLayer and add a rule for pool_update: allow, deny, rate-limit, or require approval. Point your MCP client at the PolicyLayer proxy URL and the rule is enforced on every call, before it reaches Truenas. Nothing to install.
pool_update is a Write tool with medium risk. Write tools should be rate-limited to prevent accidental bulk modifications.
Yes. Add a rate_limit block to the pool_update rule in your PolicyLayer policy. For example, setting max: 10 and window: 60 limits the tool to 10 calls per minute. Rate limits are tracked per agent session and reset automatically.
Set action: deny in the PolicyLayer policy for pool_update. The AI agent will receive a policy violation error and cannot call the tool. You can also include a reason field to explain why the tool is blocked.
pool_update is provided by the Truenas MCP server (spranab/truenas-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Start from Truenas, add the rest of your stack, and see everything your agents can call. Then put policy on all of it.
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279 Truenas tools catalogued and risk-classified — across an index of 43,000+ MCP servers.