diff --git a/src/emu/CMakeLists.txt b/src/emu/CMakeLists.txt
index 97d696b..871acf6 100644
--- a/src/emu/CMakeLists.txt
+++ b/src/emu/CMakeLists.txt
@@ -30,7 +30,6 @@ add_library(emu STATIC
   stream.c
   trace.c
   loom.c
-  metadata.c
   mux.c
   sort.c
   path.c
diff --git a/src/emu/loom.c b/src/emu/loom.c
index 99ebca8..62b1a38 100644
--- a/src/emu/loom.c
+++ b/src/emu/loom.c
@@ -70,6 +70,84 @@ loom_init_begin(struct loom *loom, const char *name)
 	return 0;
 }
 
+/* Merges the metadata CPUs with the ones in the loom */
+static int
+load_cpus(struct loom *loom, JSON_Object *meta)
+{
+	JSON_Array *cpuarray = json_object_dotget_array(meta, "ovni.loom_cpus");
+
+	/* It may not have the CPUs defined */
+	if (cpuarray == NULL)
+		return 0;
+
+	size_t ncpus = json_array_get_count(cpuarray);
+	if (ncpus == 0) {
+		err("empty 'cpus' array in metadata");
+		return -1;
+	}
+
+	for (size_t i = 0; i < ncpus; i++) {
+		JSON_Object *jcpu = json_array_get_object(cpuarray, i);
+		if (jcpu == NULL) {
+			err("json_array_get_object() failed for cpu");
+			return -1;
+		}
+
+		/* Cast from double */
+		int index = (int) json_object_get_number(jcpu, "index");
+		int phyid = (int) json_object_get_number(jcpu, "phyid");
+
+		struct cpu *cpu = loom_find_cpu(loom, phyid);
+
+		if (cpu) {
+			/* Ensure they have the same index */
+			if (cpu->index != index) {
+				err("mismatch index in existing cpu: %d", index);
+				return -1;
+			}
+
+			/* Duplicated, ignore */
+			continue;
+		}
+
+		cpu = calloc(1, sizeof(struct cpu));
+		if (cpu == NULL) {
+			err("calloc failed:");
+			return -1;
+		}
+
+		cpu_init_begin(cpu, index, phyid, 0);
+
+		if (loom_add_cpu(loom, cpu) != 0) {
+			err("loom_add_cpu() failed");
+			return -1;
+		}
+	}
+
+	return 0;
+}
+
+/** Merges the given metadata with the one stored.
+ *
+ * It is an error to provide metadata that doesn't match with the already stored
+ * in the process.
+ *
+ * Precondition: The stream ovni.part must be "thread".
+ * Precondition: The stream version must be ok.
+ */
+int
+loom_load_metadata(struct loom *loom, struct stream *s)
+{
+	JSON_Object *meta = stream_metadata(s);
+
+	if (load_cpus(loom, meta) != 0) {
+		err("cannot load loom cpus");
+		return -1;
+	}
+
+	return 0;
+}
+
 void
 loom_set_gindex(struct loom *loom, int64_t gindex)
 {
@@ -183,6 +261,44 @@ by_phyid(struct cpu *c1, struct cpu *c2)
 		return 0;
 }
 
+int
+loom_set_rank_min(struct loom *loom)
+{
+	if (loom->rank_min != INT_MAX) {
+		err("rank_min already set");
+		return -1;
+	}
+
+	/* Ensure that all processes have a rank */
+	for (struct proc *p = loom->procs; p; p = p->hh.next) {
+		if (p->rank >= 0) {
+			loom->rank_enabled = 1;
+			break;
+		}
+	}
+
+	if (!loom->rank_enabled) {
+		dbg("loom %s has no rank information", loom->name);
+		return 0;
+	}
+
+	/* Ensure that all processes have a rank */
+	for (struct proc *p = loom->procs; p; p = p->hh.next) {
+		if (p->rank < 0) {
+			err("process %s has no rank information", p->id);
+			return -1;
+		}
+
+		/* Compute rank_min for CPU sorting */
+		if (p->rank < loom->rank_min)
+			loom->rank_min = p->rank;
+	}
+
+	dbg("loom %s has rank_min %d", loom->name, loom->rank_min);
+
+	return 0;
+}
+
 void
 loom_sort(struct loom *loom)
 {
@@ -200,22 +316,22 @@ loom_sort(struct loom *loom)
 int
 loom_init_end(struct loom *loom)
 {
-	/* Set rank enabled */
-	for (struct proc *p = loom->procs; p; p = p->hh.next) {
-		if (p->rank >= 0) {
-			loom->rank_enabled = 1;
-			break;
-		}
+	/* rank_min must be set */
+	if (loom->rank_enabled && loom->rank_min == INT_MAX) {
+		err("rank_min not set");
+		return -1;
 	}
 
-	/* Ensure that all processes have a rank */
-	if (loom->rank_enabled) {
-		for (struct proc *p = loom->procs; p; p = p->hh.next) {
-			if (p->rank < 0) {
-				err("process %s has no rank information", p->id);
-				return -1;
-			}
-		}
+	/* It is not valid to define a loom without CPUs */
+	if (loom->ncpus == 0) {
+		err("loom %s has no physical CPUs", loom->name);
+		return -1;
+	}
+
+	/* Or without processes */
+	if (loom->nprocs == 0) {
+		err("loom %s has no processes", loom->name);
+		return -1;
 	}
 
 	/* Populate cpus_array */
@@ -224,6 +340,7 @@ loom_init_end(struct loom *loom)
 		err("calloc failed:");
 		return -1;
 	}
+
 	for (struct cpu *c = loom->cpus; c; c = c->hh.next) {
 		int index = cpu_get_index(c);
 		if (index < 0 || (size_t) index >= loom->ncpus) {
@@ -279,34 +396,6 @@ loom_add_proc(struct loom *loom, struct proc *proc)
 		return -1;
 	}
 
-	if (!proc->metadata_loaded) {
-		err("process %d hasn't loaded metadata", pid);
-		return -1;
-	}
-
-	if (loom->rank_enabled && proc->rank < 0) {
-		err("missing rank in process %d", pid);
-		return -1;
-	}
-
-	/* Check previous ranks if any */
-	if (!loom->rank_enabled && proc->rank >= 0) {
-		loom->rank_enabled = 1;
-
-		for (struct proc *p = loom->procs; p; p = p->hh.next) {
-			if (p->rank < 0) {
-				err("missing rank in process %d", p->pid);
-				return -1;
-			}
-
-			if (p->rank < loom->rank_min)
-				loom->rank_min = p->rank;
-		}
-	}
-
-	if (loom->rank_enabled && proc->rank < loom->rank_min)
-		loom->rank_min = proc->rank;
-
 	HASH_ADD_INT(loom->procs, pid, proc);
 	loom->nprocs++;
 
diff --git a/src/emu/loom.h b/src/emu/loom.h
index c8072a2..93575c2 100644
--- a/src/emu/loom.h
+++ b/src/emu/loom.h
@@ -53,6 +53,8 @@ struct loom {
 
 USE_RET const char *loom_name(struct stream *s);
 USE_RET int loom_init_begin(struct loom *loom, const char *name);
+USE_RET int loom_load_metadata(struct loom *loom, struct stream *s);
+USE_RET int loom_set_rank_min(struct loom *loom);
 USE_RET int loom_init_end(struct loom *loom);
 USE_RET int loom_add_cpu(struct loom *loom, struct cpu *cpu);
 USE_RET int64_t loom_get_gindex(struct loom *loom);
diff --git a/src/emu/metadata.c b/src/emu/metadata.c
deleted file mode 100644
index 43a57a2..0000000
--- a/src/emu/metadata.c
+++ /dev/null
@@ -1,116 +0,0 @@
-/* Copyright (c) 2021-2024 Barcelona Supercomputing Center (BSC)
- * SPDX-License-Identifier: GPL-3.0-or-later */
-
-#include "metadata.h"
-#include <stdlib.h>
-#include <string.h>
-#include "cpu.h"
-#include "loom.h"
-#include "ovni.h"
-#include "parson.h"
-#include "proc.h"
-#include "stream.h"
-#include "thread.h"
-
-static int
-check_version(JSON_Object *meta)
-{
-	JSON_Value *version_val = json_object_get_value(meta, "version");
-	if (version_val == NULL) {
-		err("missing attribute \"version\"");
-		return -1;
-	}
-
-	int version = (int) json_number(version_val);
-
-	if (version != OVNI_METADATA_VERSION) {
-		err("metadata version mismatch %d (expected %d)",
-				version, OVNI_METADATA_VERSION);
-		return -1;
-	}
-
-	return 0;
-}
-
-static int
-has_cpus(JSON_Object *meta)
-{
-	/* Only check for the "ovni.loom_cpus" key, if it has zero
-	 * elements is an error that will be reported later */
-	if (json_object_dotget_array(meta, "ovni.loom_cpus") != NULL)
-		return 1;
-
-	return 0;
-}
-
-static int
-load_cpus(struct loom *loom, JSON_Object *meta)
-{
-	JSON_Array *cpuarray = json_object_dotget_array(meta, "ovni.loom_cpus");
-	if (cpuarray == NULL) {
-		err("cannot find 'cpus' array");
-		return -1;
-	}
-
-	size_t ncpus = json_array_get_count(cpuarray);
-	if (ncpus == 0) {
-		err("empty 'cpus' array in metadata");
-		return -1;
-	}
-
-	if (loom->ncpus > 0) {
-		err("loom %s already has cpus", loom->id);
-		return -1;
-	}
-
-	for (size_t i = 0; i < ncpus; i++) {
-		JSON_Object *jcpu = json_array_get_object(cpuarray, i);
-		if (jcpu == NULL) {
-			err("json_array_get_object() failed for cpu");
-			return -1;
-		}
-
-		/* Cast from double */
-		int index = (int) json_object_get_number(jcpu, "index");
-		int phyid = (int) json_object_get_number(jcpu, "phyid");
-
-		struct cpu *cpu = calloc(1, sizeof(struct cpu));
-		if (cpu == NULL) {
-			err("calloc failed:");
-			return -1;
-		}
-
-		cpu_init_begin(cpu, index, phyid, 0);
-
-		if (loom_add_cpu(loom, cpu) != 0) {
-			err("loom_add_cpu() failed");
-			return -1;
-		}
-	}
-
-	return 0;
-}
-
-int
-metadata_load_proc(struct stream *s, struct loom *loom, struct proc *proc)
-{
-	JSON_Object *meta = stream_metadata(s);
-
-	if (check_version(meta) != 0) {
-		err("version check failed");
-		return -1;
-	}
-
-	/* The appid is populated from the metadata */
-	if (proc_load_metadata(proc, meta) != 0) {
-		err("cannot load process attributes");
-		return -1;
-	}
-
-	if (has_cpus(meta) && load_cpus(loom, meta) != 0) {
-		err("cannot load loom cpus");
-		return -1;
-	}
-
-	return 0;
-}
diff --git a/src/emu/metadata.h b/src/emu/metadata.h
deleted file mode 100644
index 2e1c3e7..0000000
--- a/src/emu/metadata.h
+++ /dev/null
@@ -1,14 +0,0 @@
-/* Copyright (c) 2021-2024 Barcelona Supercomputing Center (BSC)
- * SPDX-License-Identifier: GPL-3.0-or-later */
-
-#ifndef METADATA_H
-#define METADATA_H
-
-#include "common.h"
-struct stream;
-struct loom;
-struct proc;
-
-USE_RET int metadata_load_proc(struct stream *s, struct loom *loom, struct proc *proc);
-
-#endif /* METADATA_H */
diff --git a/src/emu/proc.c b/src/emu/proc.c
index f42e396..b33a5d9 100644
--- a/src/emu/proc.c
+++ b/src/emu/proc.c
@@ -32,6 +32,9 @@ proc_init_begin(struct proc *proc, int pid)
 	memset(proc, 0, sizeof(struct proc));
 
 	proc->gindex = -1;
+	proc->appid = 0;
+	proc->rank = -1;
+	proc->nranks = 0;
 	proc->pid = pid;
 
 	if (snprintf(proc->id, PATH_MAX, "proc.%d", pid) >= PATH_MAX) {
@@ -56,38 +59,105 @@ proc_set_loom(struct proc *proc, struct loom *loom)
 	proc->loom = loom;
 }
 
-int
-proc_load_metadata(struct proc *proc, JSON_Object *meta)
+static int
+load_appid(struct proc *proc, struct stream *s)
 {
-	if (proc->metadata_loaded) {
-		err("process %s already loaded metadata", proc->id);
-		return -1;
-	}
-
-	JSON_Value *version_val = json_object_get_value(meta, "version");
-	if (version_val == NULL) {
-		err("missing attribute 'version' in metadata");
-		return -1;
-	}
-
-	proc->metadata_version = (int) json_number(version_val);
-
+	JSON_Object *meta = stream_metadata(s);
 	JSON_Value *appid_val = json_object_dotget_value(meta, "ovni.app_id");
-	if (appid_val == NULL) {
-		err("missing attribute 'ovni.app_id' in metadata");
+
+	/* May not be present in all thread streams */
+	if (appid_val == NULL)
+		return 0;
+
+	int appid = (int) json_number(appid_val);
+	if (proc->appid && proc->appid != appid) {
+		err("mismatch previous appid %d with stream: %s",
+				proc->appid, s->relpath);
 		return -1;
 	}
 
-	proc->appid = (int) json_number(appid_val);
+	if (appid <= 0) {
+		err("appid must be >0, stream: %s", s->relpath);
+		return -1;
+	}
 
+	proc->appid = appid;
+	return 0;
+}
+
+static int
+load_rank(struct proc *proc, struct stream *s)
+{
+	JSON_Object *meta = stream_metadata(s);
 	JSON_Value *rank_val = json_object_dotget_value(meta, "ovni.rank");
 
-	if (rank_val != NULL)
-		proc->rank = (int) json_number(rank_val);
-	else
-		proc->rank = -1;
+	/* Optional */
+	if (rank_val == NULL) {
+		dbg("process %s has no rank", proc->id);
+		return 0;
+	}
 
-	proc->metadata_loaded = 1;
+	int rank = (int) json_number(rank_val);
+
+	if (rank < 0) {
+		err("rank %d must be >=0, stream: %s", rank, s->relpath);
+		return -1;
+	}
+
+	if (proc->rank >= 0 && proc->rank != rank) {
+		err("mismatch previous rank %d with stream: %s",
+				proc->rank, s->relpath);
+		return -1;
+	}
+
+	/* Same with nranks, but it is not optional now */
+	JSON_Value *nranks_val = json_object_dotget_value(meta, "ovni.nranks");
+	if (nranks_val == NULL) {
+		err("missing ovni.nranks attribute: %s", s->relpath);
+		return -1;
+	}
+
+	int nranks = (int) json_number(nranks_val);
+
+	if (nranks <= 0) {
+		err("nranks %d must be >0, stream: %s", nranks, s->relpath);
+		return -1;
+	}
+
+	if (proc->nranks > 0 && proc->nranks != nranks) {
+		err("mismatch previous nranks %d with stream: %s",
+				proc->nranks, s->relpath);
+		return -1;
+	}
+
+	/* Ensure rank fits in nranks */
+	if (rank >= nranks) {
+		err("rank %d must be lower than nranks %d: %s",
+				rank, nranks, s->relpath);
+		return -1;
+	}
+
+	dbg("process %s rank=%d nranks=%d",
+			proc->id, rank, nranks);
+	proc->rank = rank;
+	proc->nranks = nranks;
+
+	return 0;
+}
+
+/** Merges the metadata from the stream in the process. */
+int
+proc_load_metadata(struct proc *proc, struct stream *s)
+{
+	if (load_appid(proc, s) != 0) {
+		err("load_appid failed for stream: %s", s->relpath);
+		return -1;
+	}
+
+	if (load_rank(proc, s) != 0) {
+		err("load_rank failed for stream: %s", s->relpath);
+		return -1;
+	}
 
 	return 0;
 }
@@ -151,8 +221,8 @@ proc_init_end(struct proc *proc)
 		return -1;
 	}
 
-	if (!proc->metadata_loaded) {
-		err("metadata not loaded");
+	if (proc->appid <= 0) {
+		err("appid not set");
 		return -1;
 	}
 
diff --git a/src/emu/proc.h b/src/emu/proc.h
index 01c0fd2..7964bff 100644
--- a/src/emu/proc.h
+++ b/src/emu/proc.h
@@ -8,7 +8,6 @@
 #include <stdint.h>
 #include "common.h"
 #include "extend.h"
-#include "parson.h"
 #include "uthash.h"
 struct loom;
 struct stream;
@@ -19,12 +18,11 @@ struct proc {
 	char id[PATH_MAX];
 	int is_init;
 
-	int metadata_loaded;
-	int metadata_version;
 	int pid;
 	int index;
 	int appid;
 	int rank;
+	int nranks;
 
 	int nthreads;
 	struct thread *threads;
@@ -53,7 +51,7 @@ USE_RET int proc_get_pid(struct proc *proc);
         void proc_set_gindex(struct proc *proc, int64_t gindex);
         void proc_set_loom(struct proc *proc, struct loom *loom);
         void proc_sort(struct proc *proc);
-USE_RET int proc_load_metadata(struct proc *proc, JSON_Object *meta);
+USE_RET int proc_load_metadata(struct proc *proc, struct stream *s);
 USE_RET struct thread *proc_find_thread(struct proc *proc, int tid);
 USE_RET int proc_add_thread(struct proc *proc, struct thread *thread);
         void proc_sort(struct proc *proc);
diff --git a/src/emu/stream.c b/src/emu/stream.c
index b723c43..faaf309 100644
--- a/src/emu/stream.c
+++ b/src/emu/stream.c
@@ -148,7 +148,6 @@ load_json(const char *path)
 		return NULL;
 	}
 
-	/* TODO: Check version */
 	if (check_version(meta) != 0) {
 		err("check_version failed");
 		return NULL;
diff --git a/src/emu/system.c b/src/emu/system.c
index 247414b..86fdccc 100644
--- a/src/emu/system.c
+++ b/src/emu/system.c
@@ -11,7 +11,6 @@
 #include "cpu.h"
 #include "emu_args.h"
 #include "loom.h"
-#include "metadata.h"
 #include "proc.h"
 #include "pv/prf.h"
 #include "pv/pvt.h"
@@ -73,30 +72,30 @@ create_proc(struct loom *loom, struct stream *s)
 	}
 
 	struct proc *proc = loom_find_proc(loom, pid);
-
-	if (proc != NULL)
-		return proc;
-
-	proc = malloc(sizeof(struct proc));
-
 	if (proc == NULL) {
-		err("malloc failed:");
-		return NULL;
+		/* Create a new process */
+
+		proc = malloc(sizeof(struct proc));
+
+		if (proc == NULL) {
+			err("malloc failed:");
+			return NULL;
+		}
+
+		if (proc_init_begin(proc, pid) != 0) {
+			err("proc_init_begin failed: %s", s->relpath);
+			return NULL;
+		}
+
+		if (loom_add_proc(loom, proc) != 0) {
+			err("loom_add_proc failed");
+			return NULL;
+		}
 	}
 
-	if (proc_init_begin(proc, pid) != 0) {
-		err("proc_init_begin failed: %s", s->relpath);
-		return NULL;
-	}
-
-	/* Load metadata too */
-	if (metadata_load_proc(s, loom, proc) != 0) {
-		err("cannot load metadata from %s", s->relpath);
-		return NULL;
-	}
-
-	if (loom_add_proc(loom, proc) != 0) {
-		err("loom_add_proc failed");
+	/* The appid is populated from the metadata */
+	if (proc_load_metadata(proc, s) != 0) {
+		err("proc_load_metadata failed");
 		return NULL;
 	}
 
@@ -141,6 +140,11 @@ create_loom(struct system *sys, struct stream *s)
 		sys->nlooms++;
 	}
 
+	if (loom_load_metadata(loom, s) != 0) {
+		err("loom_load_metadata failed for stream: %s", s->relpath);
+		return NULL;
+	}
+
 	return loom;
 }
 
@@ -216,9 +220,8 @@ is_thread_stream(struct stream *s)
 		return -1;
 	}
 
-	if (strcmp(part_type, "thread") == 0) {
+	if (strcmp(part_type, "thread") == 0)
 		return 1;
-	}
 
 	return 0;
 }
@@ -235,11 +238,11 @@ create_system(struct system *sys, struct trace *trace)
 
 	size_t i = 0;
 	for (struct stream *s = trace->streams; s ; s = s->next) {
-		int m = is_thread_stream(s);
-		if (m < 0) {
+		int ok = is_thread_stream(s);
+		if (ok < 0) {
 			err("is_thread_stream failed");
 			return -1;
-		} else if (m == 0) {
+		} else if (ok == 0) {
 			warn("ignoring unknown stream %s", s->relpath);
 			continue;
 		}
@@ -250,7 +253,6 @@ create_system(struct system *sys, struct trace *trace)
 			return -1;
 		}
 
-		/* Loads metadata too */
 		struct proc *proc = create_proc(loom, s);
 		if (proc == NULL) {
 			err("create_proc failed");
@@ -272,14 +274,6 @@ create_system(struct system *sys, struct trace *trace)
 		stream_data_set(s, lpt);
 	}
 
-	/* Ensure all looms have at least one CPU */
-	for (struct loom *l = sys->looms; l; l = l->next) {
-		if (l->ncpus == 0) {
-			err("loom %s has no physical CPUs", l->id);
-			return -1;
-		}
-	}
-
 	return 0;
 }
 
@@ -557,6 +551,12 @@ set_sort_criteria(struct system *sys)
 	int some_have = 0;
 	int all_have = 1;
 	for (struct loom *l = sys->looms; l; l = l->next) {
+		/* Set the rank_min for later sorting */
+		if (loom_set_rank_min(l) != 0) {
+			err("loom_set_rank_min failed");
+			return -1;
+		}
+
 		if (l->rank_enabled)
 			some_have = 1;
 		else
diff --git a/test/emu/common/instr.h b/test/emu/common/instr.h
index 9ac5114..85f7e6a 100644
--- a/test/emu/common/instr.h
+++ b/test/emu/common/instr.h
@@ -102,7 +102,10 @@ instr_start(int rank, int nranks)
 
 	ovni_version_check();
 	ovni_proc_init(1, rankname, getpid());
-	ovni_proc_set_rank(rank, nranks);
+
+	if (nranks > 0)
+		ovni_proc_set_rank(rank, nranks);
+
 	ovni_thread_init(get_tid());
 
 	/* All ranks inform CPUs */
diff --git a/test/unit/cpu.c b/test/unit/cpu.c
index 1c94b2e..9de24fc 100644
--- a/test/unit/cpu.c
+++ b/test/unit/cpu.c
@@ -30,11 +30,9 @@ test_oversubscription(void)
 	if (proc_init_begin(&proc, 1) != 0)
 		die("proc_init_begin failed");
 
-	proc_set_gindex(&proc, 0);
+	proc.appid = 1;
 
-	/* FIXME: We shouldn't need to recreate a full process to test the CPU
-	 * affinity rules */
-	proc.metadata_loaded = 1;
+	proc_set_gindex(&proc, 0);
 
 	struct thread th0, th1;
 
diff --git a/test/unit/loom.c b/test/unit/loom.c
index c1df60e..d2fa8cc 100644
--- a/test/unit/loom.c
+++ b/test/unit/loom.c
@@ -65,7 +65,6 @@ test_duplicate_procs(struct loom *loom)
 	struct proc proc;
 	OK(loom_init_begin(loom, testloom));
 	OK(proc_init_begin(&proc, testproc));
-	proc.metadata_loaded = 1;
 	OK(loom_add_proc(loom, &proc));
 	ERR(loom_add_proc(loom, &proc));