diff --git a/src/dbnode/persist/fs/retriever_options.go b/src/dbnode/persist/fs/retriever_options.go
index 8616dd5369..9e14d2ce94 100644
--- a/src/dbnode/persist/fs/retriever_options.go
+++ b/src/dbnode/persist/fs/retriever_options.go
@@ -22,6 +22,7 @@ package fs
 
 import (
 	"errors"
+	"runtime"
 
 	"github.com/m3db/m3/src/dbnode/storage/block"
 	"github.com/m3db/m3/src/dbnode/x/xio"
@@ -30,11 +31,12 @@ import (
 )
 
 const (
-	defaultRequestPoolSize  = 16384
-	defaultFetchConcurrency = 2
+	defaultRequestPoolSize = 16384
 )
 
 var (
+	// Allow max concurrency to match available CPUs.
+	defaultFetchConcurrency    = runtime.NumCPU()
 	errBlockLeaseManagerNotSet = errors.New("block lease manager is not set")
 )
 
diff --git a/src/dbnode/persist/fs/seek_manager_test.go b/src/dbnode/persist/fs/seek_manager_test.go
index 3459e1b90a..1f63ddde33 100644
--- a/src/dbnode/persist/fs/seek_manager_test.go
+++ b/src/dbnode/persist/fs/seek_manager_test.go
@@ -34,9 +34,16 @@ import (
 	"github.com/stretchr/testify/require"
 )
 
+const (
+	defaultTestingFetchConcurrency = 2
+)
+
 var (
 	defaultTestBlockRetrieverOptions = NewBlockRetrieverOptions().
-		SetBlockLeaseManager(&block.NoopLeaseManager{})
+		SetBlockLeaseManager(&block.NoopLeaseManager{}).
+		// Default value is determined by available CPUs, but for testing
+		// we want to have this been consistent across hardware.
+		SetFetchConcurrency(defaultTestingFetchConcurrency)
 )
 
 func TestSeekerManagerCacheShardIndices(t *testing.T) {
@@ -44,18 +51,20 @@ func TestSeekerManagerCacheShardIndices(t *testing.T) {
 
 	shards := []uint32{2, 5, 9, 478, 1023}
 	m := NewSeekerManager(nil, testDefaultOpts, defaultTestBlockRetrieverOptions).(*seekerManager)
-	var byTimes []*seekersByTime
+	byTimes := make(map[uint32]*seekersByTime)
+	var mu sync.Mutex
 	m.openAnyUnopenSeekersFn = func(byTime *seekersByTime) error {
-		byTimes = append(byTimes, byTime)
+		mu.Lock()
+		byTimes[byTime.shard] = byTime
+		mu.Unlock()
 		return nil
 	}
 
 	require.NoError(t, m.CacheShardIndices(shards))
-
 	// Assert captured byTime objects match expectations
 	require.Equal(t, len(shards), len(byTimes))
-	for idx, shard := range shards {
-		byTimes[idx].shard = shard
+	for _, shard := range shards {
+		byTimes[shard].shard = shard
 	}
 
 	// Assert seeksByShardIdx match expectations
@@ -63,13 +72,14 @@ func TestSeekerManagerCacheShardIndices(t *testing.T) {
 	for _, shard := range shards {
 		shardSet[shard] = struct{}{}
 	}
+
 	for shard, byTime := range m.seekersByShardIdx {
 		_, exists := shardSet[uint32(shard)]
 		if !exists {
 			require.False(t, byTime.accessed)
 		} else {
 			require.True(t, byTime.accessed)
-			require.Equal(t, uint32(shard), byTime.shard)
+			require.Equal(t, int(shard), int(byTime.shard))
 		}
 	}
 }
@@ -96,10 +106,10 @@ func TestSeekerManagerUpdateOpenLease(t *testing.T) {
 		mock := NewMockDataFileSetSeeker(ctrl)
 		// ConcurrentClone() will be called fetchConcurrency-1 times because the original can be used
 		// as one of the clones.
-		for i := 0; i < defaultFetchConcurrency-1; i++ {
+		for i := 0; i < defaultTestingFetchConcurrency-1; i++ {
 			mock.EXPECT().ConcurrentClone().Return(mock, nil)
 		}
-		for i := 0; i < defaultFetchConcurrency; i++ {
+		for i := 0; i < defaultTestingFetchConcurrency; i++ {
 			mock.EXPECT().Close().DoAndReturn(func() error {
 				mockSeekerStatsLock.Lock()
 				numMockSeekerCloses++
@@ -125,7 +135,7 @@ func TestSeekerManagerUpdateOpenLease(t *testing.T) {
 		byTime := m.seekersByTime(shard)
 		byTime.RLock()
 		seekers := byTime.seekers[xtime.ToUnixNano(blockStart)]
-		require.Equal(t, defaultFetchConcurrency, len(seekers.active.seekers))
+		require.Equal(t, defaultTestingFetchConcurrency, len(seekers.active.seekers))
 		require.Equal(t, 0, seekers.active.volume)
 		byTime.RUnlock()
 		require.NoError(t, m.Return(shard, blockStart, seeker))
@@ -144,13 +154,13 @@ func TestSeekerManagerUpdateOpenLease(t *testing.T) {
 		byTime := m.seekersByTime(shard)
 		byTime.RLock()
 		seekers := byTime.seekers[xtime.ToUnixNano(blockStart)]
-		require.Equal(t, defaultFetchConcurrency, len(seekers.active.seekers))
+		require.Equal(t, defaultTestingFetchConcurrency, len(seekers.active.seekers))
 		require.Equal(t, 1, seekers.active.volume)
 		byTime.RUnlock()
 	}
 	// Ensure that the old seekers actually get closed.
 	mockSeekerStatsLock.Lock()
-	require.Equal(t, len(shards)*defaultFetchConcurrency, numMockSeekerCloses)
+	require.Equal(t, len(shards)*defaultTestingFetchConcurrency, numMockSeekerCloses)
 	mockSeekerStatsLock.Unlock()
 
 	// Ensure that UpdateOpenLease() ignores updates for the wrong namespace.
@@ -166,7 +176,7 @@ func TestSeekerManagerUpdateOpenLease(t *testing.T) {
 		byTime := m.seekersByTime(shard)
 		byTime.RLock()
 		seekers := byTime.seekers[xtime.ToUnixNano(blockStart)]
-		require.Equal(t, defaultFetchConcurrency, len(seekers.active.seekers))
+		require.Equal(t, defaultTestingFetchConcurrency, len(seekers.active.seekers))
 		// Should not have increased to 2.
 		require.Equal(t, 1, seekers.active.volume)
 		byTime.RUnlock()
@@ -202,7 +212,7 @@ func TestSeekerManagerBorrowOpenSeekersLazy(t *testing.T) {
 		mock := NewMockDataFileSetSeeker(ctrl)
 		mock.EXPECT().Open(gomock.Any(), gomock.Any(), gomock.Any(), gomock.Any(), gomock.Any()).Return(nil)
 		mock.EXPECT().ConcurrentClone().Return(mock, nil)
-		for i := 0; i < defaultFetchConcurrency; i++ {
+		for i := 0; i < defaultTestingFetchConcurrency; i++ {
 			mock.EXPECT().Close().Return(nil)
 			mock.EXPECT().ConcurrentIDBloomFilter().Return(nil)
 		}
@@ -220,7 +230,7 @@ func TestSeekerManagerBorrowOpenSeekersLazy(t *testing.T) {
 		byTime := m.seekersByTime(shard)
 		byTime.RLock()
 		seekers := byTime.seekers[xtime.ToUnixNano(time.Time{})]
-		require.Equal(t, defaultFetchConcurrency, len(seekers.active.seekers))
+		require.Equal(t, defaultTestingFetchConcurrency, len(seekers.active.seekers))
 		byTime.RUnlock()
 		require.NoError(t, m.Return(shard, time.Time{}, seeker))
 	}