diff --git a/container/statssum.go b/container/statssum.go
index b07ecec5..0987dfb3 100644
--- a/container/statssum.go
+++ b/container/statssum.go
@@ -118,9 +118,9 @@ func (self *percentilesContainerHandlerWrapper) StatsPercentiles() (*info.Contai
 		stats := d.(*info.ContainerStatsSample)
 		samples = append(samples, stats)
 	})
-	self.containerPercentiles.Samples = samples
 	// XXX(dengnan): probably add to StatsParameter?
 	self.containerPercentiles.FillPercentiles(
+		samples,
 		[]int{50, 80, 90, 95, 99},
 		[]int{50, 80, 90, 95, 99},
 	)
diff --git a/container/statssum_test.go b/container/statssum_test.go
index 7ccd60c0..3efab0a5 100644
--- a/container/statssum_test.go
+++ b/container/statssum_test.go
@@ -164,11 +164,13 @@ func TestSampleCpuUsage(t *testing.T) {
 		}
 	}
 
-	s, err := handler.StatsPercentiles()
+	_, err := handler.StatsPercentiles()
 	if err != nil {
 		t.Fatal(err)
 	}
-	for _, sample := range s.Samples {
+	hs := handler.(*percentilesContainerHandlerWrapper)
+	hs.sampler.Map(func(d interface{}) {
+		sample := d.(*info.ContainerStatsSample)
 		if sample.Duration != samplePeriod {
 			t.Errorf("sample duration is %v, not %v", sample.Duration, samplePeriod)
 		}
@@ -182,5 +184,5 @@ func TestSampleCpuUsage(t *testing.T) {
 		if !found {
 			t.Errorf("unable to find cpu usage %v", cpuUsage)
 		}
-	}
+	})
 }
diff --git a/info/container.go b/info/container.go
index a0c8affc..4036a56b 100644
--- a/info/container.go
+++ b/info/container.go
@@ -69,6 +69,9 @@ type ContainerInfo struct {
 	// Historical statistics gathered from the container.
 	Stats []*ContainerStats `json:"stats,omitempty"`
 
+	// Randomly sampled container states.
+	Samples []*ContainerStatsSample `json:"samples,omitempty"`
+
 	StatsPercentiles *ContainerStatsPercentiles `json:"stats_summary,omitempty"`
 }
 
@@ -177,19 +180,15 @@ type ContainerStatsSample struct {
 	} `json:"memory"`
 }
 
-// This is not exported.
-// Use FillPercentile to calculate percentiles
-type percentile struct {
+type Percentile struct {
 	Percentage int    `json:"percentage"`
 	Value      uint64 `json:"value"`
 }
 
 type ContainerStatsPercentiles struct {
-	// TODO(dengnan): More things?
-	MaxMemoryUsage         uint64                  `json:"max_memory_usage,omitempty"`
-	Samples                []*ContainerStatsSample `json:"samples,omitempty"`
-	MemoryUsagePercentiles []percentile            `json:"memory_usage_percentiles,omitempty"`
-	CpuUsagePercentiles    []percentile            `json:"cpu_usage_percentiles,omitempty"`
+	MaxMemoryUsage         uint64       `json:"max_memory_usage,omitempty"`
+	MemoryUsagePercentiles []Percentile `json:"memory_usage_percentiles,omitempty"`
+	CpuUsagePercentiles    []Percentile `json:"cpu_usage_percentiles,omitempty"`
 }
 
 // Each sample needs two stats because the cpu usage in ContainerStats is
@@ -237,11 +236,11 @@ func (self uint64Slice) Swap(i, j int) {
 	self[i], self[j] = self[j], self[i]
 }
 
-func (self uint64Slice) Percentiles(requestedPercentiles ...int) []percentile {
+func (self uint64Slice) Percentiles(requestedPercentiles ...int) []Percentile {
 	if len(self) == 0 {
 		return nil
 	}
-	ret := make([]percentile, 0, len(requestedPercentiles))
+	ret := make([]Percentile, 0, len(requestedPercentiles))
 	sort.Sort(self)
 	for _, p := range requestedPercentiles {
 		idx := (len(self) * p / 100) - 1
@@ -250,7 +249,7 @@ func (self uint64Slice) Percentiles(requestedPercentiles ...int) []percentile {
 		}
 		ret = append(
 			ret,
-			percentile{
+			Percentile{
 				Percentage: p,
 				Value:      self[idx],
 			},
@@ -259,14 +258,14 @@ func (self uint64Slice) Percentiles(requestedPercentiles ...int) []percentile {
 	return ret
 }
 
-func (self *ContainerStatsPercentiles) FillPercentiles(cpuPercentages, memoryPercentages []int) {
-	if len(self.Samples) == 0 {
+func (self *ContainerStatsPercentiles) FillPercentiles(samples []*ContainerStatsSample, cpuPercentages, memoryPercentages []int) {
+	if len(samples) == 0 {
 		return
 	}
-	cpuUsages := make([]uint64, 0, len(self.Samples))
-	memUsages := make([]uint64, 0, len(self.Samples))
+	cpuUsages := make([]uint64, 0, len(samples))
+	memUsages := make([]uint64, 0, len(samples))
 
-	for _, sample := range self.Samples {
+	for _, sample := range samples {
 		if sample == nil {
 			continue
 		}
diff --git a/storage/storage.go b/storage/storage.go
index f9990831..ca646fd6 100644
--- a/storage/storage.go
+++ b/storage/storage.go
@@ -18,4 +18,13 @@ import "github.com/google/cadvisor/info"
 
 type StorageDriver interface {
 	AddStats(ref info.ContainerReference, stats *info.ContainerStats) error
+
+	// Read most recent stats. numStats indicates max number of stats
+	// returned. The returned stats must be consecutive observed stats. If
+	// numStats < 0, then return all stats stored in the storage.
+	RecentStats(numStats int) ([]*info.ContainerStats, error)
+
+	Percentiles(cpuUsagePercentiles []int, memUsagePercentiles []int) (*info.ContainerStatsPercentiles, error)
+
+	Samples(numSamples int) ([]*info.ContainerStatsSample, error)
 }