diff --git a/internal/metamorphic/meta_test.go b/internal/metamorphic/meta_test.go
index aacf56d57e..e66984de0e 100644
--- a/internal/metamorphic/meta_test.go
+++ b/internal/metamorphic/meta_test.go
@@ -40,8 +40,8 @@ import (
 var (
 	dir = flag.String("dir", "_meta",
 		"the directory storing test state")
-	disk = flag.Bool("disk", false,
-		"whether to use an in-mem DB or on-disk (in-mem is significantly faster)")
+	fs = flag.String("fs", "rand",
+		`force the tests to use either memory or disk-backed filesystems (valid: "mem", "disk", "rand")`)
 	// TODO: default error rate to a non-zero value. Currently, retrying is
 	// non-deterministic because of the Ierator.*WithLimit() methods since
 	// they may say that the Iterator is not valid, but be positioned at a
@@ -93,7 +93,7 @@ func testMetaRun(t *testing.T, runDir string, seed uint64) {
 
 	// Set up the filesystem to use for the test. Note that by default we use an
 	// in-memory FS.
-	if *disk && !testOpts.strictFS {
+	if testOpts.useDisk {
 		opts.FS = vfs.Default
 		require.NoError(t, os.RemoveAll(opts.FS.PathJoin(runDir, "data")))
 	} else {
@@ -134,7 +134,7 @@ func testMetaRun(t *testing.T, runDir string, seed uint64) {
 		}
 	}
 
-	if *keep && !*disk {
+	if *keep && !testOpts.useDisk {
 		m.maybeSaveData()
 	}
 }
@@ -211,12 +211,23 @@ func TestMeta(t *testing.T) {
 		runDir := filepath.Join(metaDir, path.Base(t.Name()))
 		require.NoError(t, os.MkdirAll(runDir, 0755))
 
+		// If the filesystem type was forced, all tests will use that value.
+		switch *fs {
+		case "rand":
+			// No-op. Use the generated value for the filesystem.
+		case "disk":
+			opts.useDisk = true
+		case "mem":
+			opts.useDisk = false
+		default:
+			t.Fatalf("unknown forced filesystem type: %q", *fs)
+		}
+
 		optionsPath := filepath.Join(runDir, "OPTIONS")
 		optionsStr := optionsToString(opts)
 		require.NoError(t, ioutil.WriteFile(optionsPath, []byte(optionsStr), 0644))
 
 		args := []string{
-			"-disk=" + fmt.Sprint(*disk),
 			"-keep=" + fmt.Sprint(*keep),
 			"-run-dir=" + runDir,
 			"-test.run=" + rootName + "$",
diff --git a/internal/metamorphic/options.go b/internal/metamorphic/options.go
index 868eb37132..4eca1994ad 100644
--- a/internal/metamorphic/options.go
+++ b/internal/metamorphic/options.go
@@ -8,7 +8,7 @@ import (
 	"github.com/cockroachdb/pebble"
 	"github.com/cockroachdb/pebble/bloom"
 	"github.com/cockroachdb/pebble/internal/cache"
-	"github.com/cockroachdb/pebble/vfs"
+	"github.com/cockroachdb/pebble/internal/randvar"
 	"golang.org/x/exp/rand"
 )
 
@@ -42,6 +42,9 @@ func parseOptions(opts *testOptions, data string) error {
 			case "TestOptions.replace_single_delete":
 				opts.replaceSingleDelete = true
 				return true
+			case "TestOptions.use_disk":
+				opts.useDisk = true
+				return true
 			default:
 				return false
 			}
@@ -53,7 +56,7 @@ func parseOptions(opts *testOptions, data string) error {
 
 func optionsToString(opts *testOptions) string {
 	str := opts.opts.String()
-	if opts.strictFS || opts.ingestUsingApply || opts.replaceSingleDelete {
+	if opts.strictFS || opts.ingestUsingApply || opts.replaceSingleDelete || opts.useDisk {
 		str += "\n[TestOptions]\n"
 	}
 	if opts.strictFS {
@@ -65,13 +68,15 @@ func optionsToString(opts *testOptions) string {
 	if opts.replaceSingleDelete {
 		str += "  replace_single_delete=true\n"
 	}
+	if opts.useDisk {
+		str += "  use_disk=true\n"
+	}
 	return str
 }
 
 func defaultOptions() *pebble.Options {
 	opts := &pebble.Options{
 		Comparer: &comparer,
-		FS:       vfs.NewMem(),
 		Levels: []pebble.LevelOptions{{
 			FilterPolicy: bloom.FilterPolicy(10),
 		}},
@@ -82,6 +87,7 @@ func defaultOptions() *pebble.Options {
 
 type testOptions struct {
 	opts     *pebble.Options
+	useDisk  bool
 	strictFS bool
 	// Use Batch.Apply rather than DB.Ingest.
 	ingestUsingApply bool
@@ -177,6 +183,10 @@ func standardOptions() []*testOptions {
 		20: `
 [TestOptions]
   replace_single_delete=true
+`,
+		21: `
+[TestOptions]
+  use_disk=true
 `,
 	}
 
@@ -221,7 +231,10 @@ func randomOptions(rng *rand.Rand) *testOptions {
 	opts.Levels = []pebble.LevelOptions{lopts}
 
 	testOpts.opts = opts
-	testOpts.strictFS = rng.Intn(2) != 0
+	testOpts.useDisk = randvar.NewWeighted(rng, 0.9, 0.1).Int() == 1 // Use disk 10% of the time.
+	if !testOpts.useDisk {
+		testOpts.strictFS = rng.Intn(2) != 0 // Only relevant for MemFS.
+	}
 	if testOpts.strictFS {
 		opts.DisableWAL = false
 	}