diff --git a/apps/docs/docs/integrations/truenas/index.mdx b/apps/docs/docs/integrations/truenas/index.mdx
index 5d29a7019..5e57f3a89 100644
--- a/apps/docs/docs/integrations/truenas/index.mdx
+++ b/apps/docs/docs/integrations/truenas/index.mdx
@@ -27,6 +27,8 @@ import Alert from '@theme/Admonition';
       ]}
 />
 
+The storage values shown by these widgets use the root ZFS dataset's usable `used` and `available` space, including RAIDZ parity overhead and dataset limits.
+
 ### Adding the integration
 <AddingIntegration />
 
diff --git a/packages/integrations/src/truenas/test/truenas-integration.spec.ts b/packages/integrations/src/truenas/test/truenas-integration.spec.ts
index 91ab0662c..7f1a2ad4e 100644
--- a/packages/integrations/src/truenas/test/truenas-integration.spec.ts
+++ b/packages/integrations/src/truenas/test/truenas-integration.spec.ts
@@ -148,6 +148,14 @@ const happyResponder = (method: string) => {
       ];
     case "pool.query":
       return [{ name: "tank", status: "ONLINE", healthy: true, free: 500, size: 1000, allocated: 500 }];
+    case "pool.dataset.query":
+      return [
+        {
+          id: "tank",
+          used: { parsed: 200 },
+          available: { parsed: 300 },
+        },
+      ];
     case "interface.query":
       return [{ id: "eth0", name: "eth0" }];
     case "reporting.netdata_get_data":
@@ -204,8 +212,8 @@ describe("TrueNasIntegration", () => {
       loadAverage: null,
       gpu: [],
       network: { up: 20_000, down: 10_000 },
-      // `available` is the free space left on the pool (free = 500), not its total size.
-      fileSystem: [{ deviceName: "tank", available: "500", used: "500", percentage: 50 }],
+      // `available` and `used` come from the root dataset, not the physical pool.
+      fileSystem: [{ deviceName: "tank", available: "300", used: "200", percentage: 40 }],
       smart: [{ deviceName: "tank", healthy: true, overallStatus: "ONLINE", temperature: null }],
     });
   });
diff --git a/packages/integrations/src/truenas/truenas-integration.ts b/packages/integrations/src/truenas/truenas-integration.ts
index 21f526201..6a5249a2e 100644
--- a/packages/integrations/src/truenas/truenas-integration.ts
+++ b/packages/integrations/src/truenas/truenas-integration.ts
@@ -49,9 +49,9 @@ export class TrueNasIntegration extends Integration implements ISystemHealthMoni
       memUsedInBytes,
       fileSystem: datasets.map((dataset) => ({
         deviceName: dataset.name,
-        available: `${dataset.free}`, // free space left on the pool
-        used: `${dataset.allocated}`,
-        percentage: (dataset.allocated / dataset.size) * 100,
+        available: `${dataset.available}`,
+        used: `${dataset.used}`,
+        percentage: (dataset.used / (dataset.used + dataset.available)) * 100,
       })),
       availablePkgUpdates: 0,
       network: {
@@ -117,12 +117,40 @@ export class TrueNasIntegration extends Integration implements ISystemHealthMoni
         return null;
       })
       .filter((pool) => pool !== null);
+
+    if (activePools.length === 0) return [];
+
+    const datasets = await this.requestAsync("pool.dataset.query", [
+      [["id", "IN", activePools.map((pool) => pool.name)]],
+      {
+        extra: {
+          properties: ["used", "available"],
+        },
+      },
+    ]);
+    const parsedDatasets = await poolDatasetSchema.parseAsync(datasets);
+
+    const poolsWithUsableSpace = activePools
+      .map((pool) => {
+        const dataset = parsedDatasets.find((candidate) => candidate.id === pool.name);
+        if (!dataset || dataset.used.parsed === null || dataset.available.parsed === null) return null;
+
+        return {
+          name: pool.name,
+          status: pool.status,
+          healthy: pool.healthy,
+          used: dataset.used.parsed,
+          available: dataset.available.parsed,
+        };
+      })
+      .filter((pool) => pool !== null);
+
     logger.debug("Retrieved pools", {
       url: this.integration.url,
       totalCount: result.length,
-      activeCount: activePools.length,
+      activeCount: poolsWithUsableSpace.length,
     });
-    return activePools;
+    return poolsWithUsableSpace;
   }
 
   /**
@@ -263,6 +291,14 @@ const poolSchema = z.array(
   }),
 );
 
+const poolDatasetSchema = z.array(
+  z.object({
+    id: z.string(),
+    used: z.object({ parsed: z.number().min(0).nullable() }),
+    available: z.object({ parsed: z.number().min(0).nullable() }),
+  }),
+);
+
 const reportingNetDataSchema = z.array(
   z.object({
     name: z.string(),