diff --git a/elan/rpc/rpc.go b/elan/rpc/rpc.go
index fdd46f98..5dd67f7f 100644
--- a/elan/rpc/rpc.go
+++ b/elan/rpc/rpc.go
@@ -10,6 +10,7 @@ import (
 	"crypto/sha256"
 	"encoding/hex"
 	"fmt"
+	"google.golang.org/grpc/metadata"
 	"io"
 	"io/ioutil"
 	"net"
@@ -240,6 +241,16 @@ func (s *server) GetCapabilities(ctx context.Context, req *pb.GetCapabilitiesReq
 }
 
 func (s *server) GetActionResult(ctx context.Context, req *pb.GetActionResultRequest) (*pb.ActionResult, error) {
+	md, _ := metadata.FromIncomingContext(ctx)
+	callers := md.Get("mettle-caller-name")
+
+	caller := ""
+	if len(callers) > 0 && callers[0] != "" {
+		caller = callers[0]
+	} else {
+		// Be paranoid and assume that a client may not have updated, and set the caller to the instance name
+		caller = req.InstanceName
+	}
 	ctx, cancel := context.WithTimeout(ctx, timeout)
 	defer cancel()
 	ar := &pb.ActionResult{}
@@ -256,7 +267,8 @@ func (s *server) GetActionResult(ctx context.Context, req *pb.GetActionResultReq
 			ar.StdoutRaw = b
 		}
 	}
-	if s.isFileStorage && req.InstanceName != "purity-gc" {
+
+	if s.isFileStorage && caller != "purity-gc" {
 		now := time.Now()
 		if err := os.Chtimes(path.Join(s.storageRoot, s.key("ac", req.ActionDigest)), now, now); err != nil {
 			log.Warning("Failed to change times on file: %s", err)
diff --git a/proto/purity/purity.proto b/proto/purity/purity.proto
index 14e37543..6f701bf0 100644
--- a/proto/purity/purity.proto
+++ b/proto/purity/purity.proto
@@ -16,6 +16,8 @@ service GC {
 message ListRequest {
   // The prefix of blobs to list. Should be exactly two hex characters.
   string prefix = 1;
+  // The instance name for the CAS server.
+  string instance_name = 2;
 }
 
 message ListResponse {
@@ -53,6 +55,8 @@ message DeleteRequest {
   // False gives the server an option to 'soft' delete them (however it may
   // interpret that).
   bool hard = 4;
+  // The instance name for the CAS server.
+  string instance_name = 5;
 }
 
 message DeleteResponse {}
diff --git a/purity/gc/gc.go b/purity/gc/gc.go
index bb0ed424..57dc8f10 100644
--- a/purity/gc/gc.go
+++ b/purity/gc/gc.go
@@ -5,6 +5,7 @@ import (
 	"context"
 	"encoding/hex"
 	"fmt"
+	"google.golang.org/grpc/metadata"
 	"path"
 	"sort"
 	"sync"
@@ -124,6 +125,8 @@ type Action struct {
 	InputSize, OutputSize int
 }
 
+const name = "purity-gc"
+
 type collector struct {
 	client            *client.Client
 	gcclient          ppb.GCClient
@@ -187,6 +190,7 @@ func (c *collector) LoadAllBlobs() error {
 			for j := 0; j < 16; j++ {
 				ctx, cancel := context.WithTimeout(context.Background(), 30*time.Minute)
 				defer cancel()
+				ctx = metadata.NewOutgoingContext(ctx, metadata.Pairs("mettle-caller-name", name))
 				resp, err := c.gcclient.List(ctx, &ppb.ListRequest{
 					Prefix: hex.EncodeToString([]byte{byte(i*16 + j)}),
 				})
@@ -475,6 +479,7 @@ func (c *collector) ReplicateBlobs(rf int) error {
 	if err := c.replicateBlobs("blobs", blobs, func(dg *pb.Digest) error {
 		ctx, cancel := context.WithTimeout(context.Background(), 10*time.Minute)
 		defer cancel()
+		ctx = metadata.NewOutgoingContext(ctx, metadata.Pairs("mettle-caller-name", name))
 		blob, _, err := c.client.ReadBlob(ctx, digest.NewFromProtoUnvalidated(dg))
 		if err != nil {
 			return err
@@ -487,6 +492,7 @@ func (c *collector) ReplicateBlobs(rf int) error {
 	return c.replicateBlobs("action results", ars, func(dg *pb.Digest) error {
 		ctx, cancel := context.WithTimeout(context.Background(), 1*time.Minute)
 		defer cancel()
+		ctx = metadata.NewOutgoingContext(ctx, metadata.Pairs("mettle-caller-name", name))
 		ar, err := c.client.GetActionResult(ctx, &pb.GetActionResultRequest{
 			InstanceName: c.client.InstanceName,
 			ActionDigest: dg,
@@ -616,6 +622,7 @@ func (c *collector) BlobUsage() ([]Blob, error) {
 func (c *collector) inputDirs(ar *ppb.ActionResult) (*pb.Action, []*pb.Directory, error) {
 	ctx, cancel := context.WithTimeout(context.Background(), 1*time.Minute)
 	defer cancel()
+	ctx = metadata.NewOutgoingContext(ctx, metadata.Pairs("mettle-caller-name", name))
 	action := &pb.Action{}
 	blob, present := c.allBlobs[ar.Hash]
 	if !present {
diff --git a/purity/main.go b/purity/main.go
index 9e8b589e..9660f188 100644
--- a/purity/main.go
+++ b/purity/main.go
@@ -20,7 +20,7 @@ var opts = struct {
 	Logging cli.LoggingOpts `group:"Options controlling logging output"`
 	GC      struct {
 		URL          string `short:"u" long:"url" required:"true" description:"URL for the storage server"`
-		InstanceName string `short:"i" long:"instance_name" default:"purity-gc" description:"Name of this execution instance"`
+		InstanceName string `short:"i" long:"instance_name" default:"mettle" description:"Name of this execution instance"`
 		TokenFile    string `long:"token_file" description:"File containing token to authenticate gRPC requests with"`
 		TLS          bool   `long:"tls" description:"Use TLS for communicating with the storage server"`
 	} `group:"Options controlling GC settings"`