From f3beb1236a34e14d775970b07fedac7e55fb111e Mon Sep 17 00:00:00 2001
From: Poorna Krishnamoorthy <poornas@users.noreply.github.com>
Date: Mon, 7 Dec 2020 16:35:11 -0800
Subject: [PATCH] Add cache usage, total capacity to prometheus metrics
 (#11026)

---
 cmd/disk-cache-stats.go           |  4 ++++
 cmd/disk-cache.go                 |  4 ++++
 cmd/metrics.go                    | 20 ++++++++++++++++++++
 docs/metrics/prometheus/README.md |  2 ++
 4 files changed, 30 insertions(+)

diff --git a/cmd/disk-cache-stats.go b/cmd/disk-cache-stats.go
index 2cf15fa2d..ff831e13b 100644
--- a/cmd/disk-cache-stats.go
+++ b/cmd/disk-cache-stats.go
@@ -23,6 +23,10 @@ import (
 // CacheDiskStats represents cache disk statistics
 // such as current disk usage and available.
 type CacheDiskStats struct {
+	// used cache size
+	UsageSize uint64
+	// total cache disk capacity
+	TotalCapacity uint64
 	// indicates if usage is high or low, if high value is '1', if low its '0'
 	UsageState int32
 	// indicates the current usage percentage of this cache disk
diff --git a/cmd/disk-cache.go b/cmd/disk-cache.go
index 97f8b18f7..bb6f59a0b 100644
--- a/cmd/disk-cache.go
+++ b/cmd/disk-cache.go
@@ -781,6 +781,10 @@ func newServerCacheObjects(ctx context.Context, config cache.Config) (CacheObjec
 			dcache := c.cache[i]
 			cacheDiskStats[i] = CacheDiskStats{}
 			if dcache != nil {
+				info, err := getDiskInfo(dcache.dir)
+				logger.LogIf(ctx, err)
+				cacheDiskStats[i].UsageSize = info.Used
+				cacheDiskStats[i].TotalCapacity = info.Total
 				cacheDiskStats[i].Dir = dcache.stats.Dir
 				atomic.StoreInt32(&cacheDiskStats[i].UsageState, atomic.LoadInt32(&dcache.stats.UsageState))
 				atomic.StoreUint64(&cacheDiskStats[i].UsagePercent, atomic.LoadUint64(&dcache.stats.UsagePercent))
diff --git a/cmd/metrics.go b/cmd/metrics.go
index 2fbfea177..21d82fef5 100644
--- a/cmd/metrics.go
+++ b/cmd/metrics.go
@@ -280,6 +280,26 @@ func cacheMetricsPrometheus(ch chan<- prometheus.Metric) {
 			float64(cdStats.UsageState),
 			cdStats.Dir,
 		)
+
+		ch <- prometheus.MustNewConstMetric(
+			prometheus.NewDesc(
+				prometheus.BuildFQName("cache", "usage", "size"),
+				"Indicates current cache usage in bytes",
+				[]string{"disk"}, nil),
+			prometheus.GaugeValue,
+			float64(cdStats.UsageSize),
+			cdStats.Dir,
+		)
+
+		ch <- prometheus.MustNewConstMetric(
+			prometheus.NewDesc(
+				prometheus.BuildFQName("cache", "total", "size"),
+				"Indicates total size of cache disk",
+				[]string{"disk"}, nil),
+			prometheus.GaugeValue,
+			float64(cdStats.TotalCapacity),
+			cdStats.Dir,
+		)
 	}
 }
 
diff --git a/docs/metrics/prometheus/README.md b/docs/metrics/prometheus/README.md
index 6b33f99f4..d8ff49033 100644
--- a/docs/metrics/prometheus/README.md
+++ b/docs/metrics/prometheus/README.md
@@ -198,6 +198,8 @@ MinIO Gateway instances enabled with Disk-Caching expose caching related metrics
 | `cache_data_served`  | Total number of bytes served from cache           |
 
 #### Per disk cache metrics
+| `cache_usage_size` | Total cache usage in bytes                                                     |
+| `cache_total_capacity` | Total size of cache disk                                                     |
 | `cache_usage_percent` | Total percentage cache usage                                                     |
 | `cache_usage_state`   | Indicates cache usage is high or low, relative to current cache 'quota' settings |