diff --git a/app/forms/disk-attach.tsx b/app/forms/disk-attach.tsx
index e4f8268b4..75f319c66 100644
--- a/app/forms/disk-attach.tsx
+++ b/app/forms/disk-attach.tsx
@@ -9,16 +9,55 @@ import { useQuery } from '@tanstack/react-query'
 import { useMemo } from 'react'
 import { useForm } from 'react-hook-form'
 
-import { api, q, type ApiError, type DiskType } from '@oxide/api'
+import {
+  api,
+  q,
+  queryClient,
+  useApiMutation,
+  type ApiError,
+  type DiskType,
+} from '@oxide/api'
 
 import { ComboboxField } from '~/components/form/fields/ComboboxField'
 import { ModalForm } from '~/components/form/ModalForm'
-import { useProjectSelector } from '~/hooks/use-params'
+import { HL } from '~/components/HL'
+import { useInstanceSelector, useProjectSelector } from '~/hooks/use-params'
+import { addToast } from '~/stores/toast'
 import { toComboboxItems } from '~/ui/lib/Combobox'
 import { ALL_ISH } from '~/util/consts'
 
 const defaultValues = { name: '' }
 
+/**
+ * Attach modal for the instance storage tab. Owns the attach mutation so its
+ * loading and error state can't outlive the modal. `AttachDiskModalForm` below
+ * stays mutation-free because the instance create form also uses it (with a
+ * setState `onSubmit`) on a route where no instance exists yet.
+ */
+export function AttachDiskModal({ onDismiss }: { onDismiss: () => void }) {
+  const { project, instance } = useInstanceSelector()
+
+  const attachDisk = useApiMutation(api.instanceDiskAttach, {
+    onSuccess(disk) {
+      queryClient.invalidateEndpoint('instanceDiskList')
+      onDismiss()
+      // prettier-ignore
+      addToast(<>Disk <HL>{disk.name}</HL> attached</>)
+    },
+  })
+
+  return (
+    <AttachDiskModalForm
+      onDismiss={onDismiss}
+      onSubmit={({ name }) => {
+        attachDisk.mutate({ path: { instance }, query: { project }, body: { disk: name } })
+      }}
+      loading={attachDisk.isPending}
+      submitError={attachDisk.error}
+    />
+  )
+}
+
 type AttachDiskProps = {
   /** If defined, this overrides the usual mutation */
   onSubmit: (diskAttach: { name: string; size: number; diskType: DiskType }) => void
diff --git a/app/pages/project/instances/StorageTab.tsx b/app/pages/project/instances/StorageTab.tsx
index 23922a4db..516a485b6 100644
--- a/app/pages/project/instances/StorageTab.tsx
+++ b/app/pages/project/instances/StorageTab.tsx
@@ -25,7 +25,7 @@ import { Storage24Icon } from '@oxide/design-system/icons/react'
 
 import { HL } from '~/components/HL'
 import { DiskStateBadge, DiskTypeBadge, ReadOnlyBadge } from '~/components/StateBadge'
-import { AttachDiskModalForm } from '~/forms/disk-attach'
+import { AttachDiskModal } from '~/forms/disk-attach'
 import { CreateDiskSideModalForm } from '~/forms/disk-create'
 import { getInstanceSelector, useInstanceSelector } from '~/hooks/use-params'
 import { useQuickActions } from '~/hooks/use-quick-actions'
@@ -320,14 +320,22 @@ export default function StorageTab() {
     ]
   )
 
-  const attachDisk = useApiMutation(api.instanceDiskAttach, {
+  // attach step of the create-then-attach flow only; the attach modal owns its
+  // own mutation. The create modal closes on create success, so this runs in
+  // the background and failures must surface as a toast.
+  const attachCreatedDisk = useApiMutation(api.instanceDiskAttach, {
     onSuccess(disk) {
       queryClient.invalidateEndpoint('instanceDiskList')
-      setShowDiskCreate(false)
-      setShowDiskAttach(false)
       // prettier-ignore
       addToast(<>Disk <HL>{disk.name}</HL> attached</>)
     },
+    onError(err, variables) {
+      addToast({
+        title: `Failed to attach disk ${variables.body.disk}`,
+        content: err.message,
+        variant: 'error',
+      })
+    },
   })
 
   const bootDisksTable = useReactTable({
@@ -434,24 +442,11 @@ export default function StorageTab() {
           onSuccess={({ name }) => {
             // TODO: this should probably be done with `mutateAsync` and
             // awaited, but it's a pain, so punt for now
-            attachDisk.mutate({ ...instancePathQuery, body: { disk: name } })
-          }}
-        />
-      )}
-      {showDiskAttach && (
-        <AttachDiskModalForm
-          onDismiss={() => {
-            setShowDiskAttach(false)
-            // clear API errors on the mutation
-            attachDisk.reset()
-          }}
-          onSubmit={({ name }) => {
-            attachDisk.mutate({ ...instancePathQuery, body: { disk: name } })
+            attachCreatedDisk.mutate({ ...instancePathQuery, body: { disk: name } })
           }}
-          loading={attachDisk.isPending}
-          submitError={attachDisk.error}
         />
       )}
+      {showDiskAttach && <AttachDiskModal onDismiss={() => setShowDiskAttach(false)} />}
       {selectedDisk && (
         <DiskDetailSideModal
           disk={selectedDisk}