diff --git a/swh/storage/backfill.py b/swh/storage/backfill.py
--- a/swh/storage/backfill.py
+++ b/swh/storage/backfill.py
@@ -80,7 +80,15 @@
         "reason",
     ],
     "directory": ["id", "dir_entries", "file_entries", "rev_entries", "raw_manifest"],
-    "extid": ["extid_type", "extid", "extid_version", "target_type", "target"],
+    "extid": [
+        "extid_type",
+        "extid",
+        "extid_version",
+        "target_type",
+        "target",
+        "payload_type",
+        "payload",
+    ],
     "metadata_authority": ["type", "url"],
     "metadata_fetcher": ["name", "version"],
     "origin": ["url"],
diff --git a/swh/storage/cassandra/cql.py b/swh/storage/cassandra/cql.py
--- a/swh/storage/cassandra/cql.py
+++ b/swh/storage/cassandra/cql.py
@@ -1352,6 +1352,8 @@
         extid: bytes,
         extid_version: int,
         target: CoreSWHID,
+        payload_type: str,
+        payload: Sha1Git,
         *,
         statement,
     ) -> Optional[ExtIDRow]:
@@ -1364,6 +1366,8 @@
                     extid_version,
                     target.object_type.value,
                     target.object_id,
+                    payload_type,
+                    payload,
                 ],
             ),
         )
diff --git a/swh/storage/cassandra/model.py b/swh/storage/cassandra/model.py
--- a/swh/storage/cassandra/model.py
+++ b/swh/storage/cassandra/model.py
@@ -317,13 +317,23 @@
 @dataclasses.dataclass
 class ExtIDRow(BaseRow):
     TABLE = "extid"
-    PARTITION_KEY = ("target", "target_type", "extid_version", "extid", "extid_type")
+    PARTITION_KEY = (
+        "target",
+        "target_type",
+        "extid_version",
+        "extid",
+        "extid_type",
+        "payload_type",
+        "payload",
+    )
 
     extid_type: str
     extid: bytes
     extid_version: int
     target_type: str
     target: bytes
+    payload_type: Optional[str]
+    payload: Optional[bytes]
 
 
 @dataclasses.dataclass
diff --git a/swh/storage/cassandra/schema.py b/swh/storage/cassandra/schema.py
--- a/swh/storage/cassandra/schema.py
+++ b/swh/storage/cassandra/schema.py
@@ -278,7 +278,9 @@
     extid_version   smallint,
     target_type     ascii,
     target          blob,
-    PRIMARY KEY ((extid_type, extid), extid_version, target_type, target)
+    payload_type    ascii,
+    payload         blob,
+    PRIMARY KEY ((extid_type, extid), extid_version, target_type, target, payload_type, payload)
 );""",
     """
 CREATE TABLE IF NOT EXISTS extid_by_target (
diff --git a/swh/storage/cassandra/storage.py b/swh/storage/cassandra/storage.py
--- a/swh/storage/cassandra/storage.py
+++ b/swh/storage/cassandra/storage.py
@@ -1663,6 +1663,8 @@
                     extid_version=extid.extid_version,
                     extid=extid.extid,
                     target=extid.target,
+                    payload_type=extid.payload_type,
+                    payload=extid.payload,
                 )
             ]
         else:
@@ -1676,12 +1678,16 @@
             target = extid.target.object_id
             extid_version = extid.extid_version
             extid_type = extid.extid_type
+            payload_type = extid.payload_type
+            payload = extid.payload
             extidrow = ExtIDRow(
                 extid_type=extid_type,
                 extid_version=extid_version,
                 extid=extid.extid,
                 target_type=target_type,
                 target=target,
+                payload_type=payload_type,
+                payload=payload,
             )
             (token, insertion_finalizer) = self._cql_runner.extid_add_prepare(extidrow)
             indexrow = ExtIDByTargetRow(
@@ -1714,6 +1720,8 @@
                         object_type=extidrow.target_type,
                         object_id=extidrow.target,
                     ),
+                    payload_type=extidrow.payload_type,
+                    payload=extidrow.payload,
                 )
                 for extidrow in extidrows
             )
@@ -1749,6 +1757,8 @@
                         object_type=SwhidObjectType(extidrow.target_type),
                         object_id=extidrow.target,
                     ),
+                    payload_type=extidrow.payload_type,
+                    payload=extidrow.payload,
                 )
                 for extidrow in extidrows
             )
diff --git a/swh/storage/in_memory.py b/swh/storage/in_memory.py
--- a/swh/storage/in_memory.py
+++ b/swh/storage/in_memory.py
@@ -740,6 +740,8 @@
         extid: bytes,
         extid_version: int,
         target: ExtendedSWHID,
+        payload_type: str,
+        payload: Sha1Git,
     ) -> Optional[ExtIDRow]:
         primary_key = self._extid.primary_key_from_dict(
             dict(
@@ -748,6 +750,8 @@
                 extid_version=extid_version,
                 target_type=target.object_type.value,
                 target=target.object_id,
+                payload_type=payload_type,
+                payload=payload,
             )
         )
         return self._extid.get_from_primary_key(primary_key)
diff --git a/swh/storage/postgresql/converters.py b/swh/storage/postgresql/converters.py
--- a/swh/storage/postgresql/converters.py
+++ b/swh/storage/postgresql/converters.py
@@ -359,4 +359,6 @@
             object_id=row["target"],
             object_type=SwhidObjectType[row["target_type"].upper()],
         ),
+        payload_type=row["payload_type"],
+        payload=row["payload"],
     )
diff --git a/swh/storage/postgresql/db.py b/swh/storage/postgresql/db.py
--- a/swh/storage/postgresql/db.py
+++ b/swh/storage/postgresql/db.py
@@ -899,7 +899,15 @@
             ((sortkey, id) for sortkey, id in enumerate(revisions)),
         )
 
-    extid_cols = ["extid", "extid_version", "extid_type", "target", "target_type"]
+    extid_cols = [
+        "extid",
+        "extid_version",
+        "extid_type",
+        "target",
+        "target_type",
+        "payload_type",
+        "payload",
+    ]
 
     def extid_get_from_extid_list(
         self, extid_type: str, ids: List[bytes], version: Optional[int] = None, cur=None
diff --git a/swh/storage/postgresql/storage.py b/swh/storage/postgresql/storage.py
--- a/swh/storage/postgresql/storage.py
+++ b/swh/storage/postgresql/storage.py
@@ -108,7 +108,7 @@
 class Storage:
     """SWH storage datastore proxy, encompassing DB and object storage"""
 
-    current_version: int = 186
+    current_version: int = 187
 
     def __init__(
         self,
@@ -807,6 +807,8 @@
                 "extid_version": getattr(extid, "extid_version", 0),
                 "target": extid.target.object_id,
                 "target_type": extid.target.object_type.name.lower(),  # arghh
+                "payload_type": extid.payload_type,
+                "payload": extid.payload,
             }
             for extid in ids
         ]
diff --git a/swh/storage/sql/30-schema.sql b/swh/storage/sql/30-schema.sql
--- a/swh/storage/sql/30-schema.sql
+++ b/swh/storage/sql/30-schema.sql
@@ -506,7 +506,9 @@
   extid       bytea not null,
   target_type object_type not null,
   target      sha1_git not null,
-  extid_version bigint not null default 0
+  extid_version bigint not null default 0,
+  payload_type text,
+  payload     sha1_git
 );
 
 comment on table extid is 'Correspondance SWH object (SWHID) <-> original revision id (vcs id)';
@@ -515,3 +517,5 @@
 comment on column extid.target_type is 'Type of SWHID of the referenced SWH object';
 comment on column extid.target is 'Value (hash) of SWHID of the refenced SWH object';
 comment on column extid.extid_version is 'Version of the extid type for the given original object';
+comment on column extid.payload_type is 'The type of the payload object';
+comment on column extid.payload is 'Content object ID of data associated with the ExtID';
diff --git a/swh/storage/sql/40-funcs.sql b/swh/storage/sql/40-funcs.sql
--- a/swh/storage/sql/40-funcs.sql
+++ b/swh/storage/sql/40-funcs.sql
@@ -598,8 +598,8 @@
     language plpgsql
 as $$
 begin
-    insert into extid (extid_type, extid, extid_version, target_type, target)
-        select distinct t.extid_type, t.extid, t.extid_version, t.target_type, t.target
+    insert into extid (extid_type, extid, extid_version, target_type, target, payload_type, payload)
+        select distinct t.extid_type, t.extid, t.extid_version, t.target_type, t.target, t.payload_type, t.payload
         from tmp_extid t
 		on conflict do nothing;
     return;
diff --git a/swh/storage/sql/60-indexes.sql b/swh/storage/sql/60-indexes.sql
--- a/swh/storage/sql/60-indexes.sql
+++ b/swh/storage/sql/60-indexes.sql
@@ -318,6 +318,14 @@
 
 -- extid
 
+-- the payload can be null if and only if the payload_type is null
+alter table extid
+  add constraint extid_payload_check
+  check ((payload_type is null) = (payload is null))
+  not valid;
+
 -- used to query by (extid_type, extid) + to deduplicate the whole row
-create unique index concurrently on extid(extid_type, extid, extid_version, target_type, target);
+create unique index concurrently on extid(extid_type, extid, extid_version, target_type, target) where payload_type is null and payload is null;
+create unique index concurrently on extid(extid_type, extid, extid_version, target_type, target, payload_type, payload) where payload_type is not null and payload is not null;
+
 create index concurrently on extid(target_type, target);
diff --git a/swh/storage/sql/upgrades/187.sql b/swh/storage/sql/upgrades/187.sql
new file mode 100644
--- /dev/null
+++ b/swh/storage/sql/upgrades/187.sql
@@ -0,0 +1,51 @@
+-- SWH DB schema upgrade
+-- from_version: 186
+-- to_version: 187
+-- description: Add payloads to ExtIDs
+
+insert into dbversion(version, release, description)
+    values(187, now(), 'Work In Progress');
+
+-- Add payload_type and payload columns.
+
+alter table extid
+  add column payload_type text;
+comment on column extid.payload_type is 'The type of the payload object';
+
+alter table extid
+  add column payload sha1_git;
+comment on column extid.payload is 'Content object ID of data associated with the ExtID';
+
+-- Add payload constraint.
+
+alter table extid
+  add constraint extid_payload_check
+  check ((payload_type is null) = (payload is null))
+  not valid;
+
+-- Update the unique index.
+
+create unique index concurrently extid_no_payload_idx
+  on extid(extid_type, extid, extid_version, target_type, target)
+  where payload_type is null and payload is null;
+
+create unique index concurrently extid_payload_idx
+  on extid(extid_type, extid, extid_version, target_type, target, payload_type, payload)
+  where payload_type is not null and payload is not null;
+
+drop index if exists extid_extid_type_extid_extid_version_target_type_target_idx;
+
+-- Update the swh_extid_add procedure to include the new columns.
+
+create or replace function swh_extid_add()
+    returns void
+    language plpgsql
+as $$
+begin
+    insert into extid (extid_type, extid, extid_version, target_type, target, payload_type, payload)
+        select distinct t.extid_type, t.extid, t.extid_version, t.target_type, t.target, t.payload_type, t.payload
+        from tmp_extid t
+		on conflict do nothing;
+    return;
+end
+$$;
diff --git a/swh/storage/tests/storage_data.py b/swh/storage/tests/storage_data.py
--- a/swh/storage/tests/storage_data.py
+++ b/swh/storage/tests/storage_data.py
@@ -831,9 +831,20 @@
         extid_version=2,
     )
 
+    extid5 = ExtID(
+        target=CoreSWHID(
+            object_type=SwhidObjectType.DIRECTORY, object_id=directory2.id
+        ),
+        extid_type="directory",
+        extid=b"something",
+        payload_type="test",
+        payload=content.sha1_git,
+    )
+
     extids: Tuple[ExtID, ...] = (
         extid1,
         extid2,
         extid3,
         extid4,
+        extid5,
     )
diff --git a/swh/storage/tests/storage_tests.py b/swh/storage/tests/storage_tests.py
--- a/swh/storage/tests/storage_tests.py
+++ b/swh/storage/tests/storage_tests.py
@@ -1695,6 +1695,41 @@
                 ObjectType.REVISION, [ids[0]], extid_type="git"
             )
 
+    def test_extid_payload(self, swh_storage, sample_data):
+        target = sample_data.directory2.swhid()
+        extids = [
+            ExtID(
+                extid=b"abc123",
+                extid_type="test",
+                target=target,
+                payload_type="test_payload",
+                payload=sample_data.content.sha1_git,
+            ),
+        ]
+
+        assert swh_storage.extid_get_from_extid("test", [b"abc123"]) == []
+        assert (
+            swh_storage.extid_get_from_target(target.object_type, [target.object_id])
+            == []
+        )
+
+        summary = swh_storage.extid_add(extids)
+        assert summary == {"extid:add": 1}
+
+        assert swh_storage.extid_get_from_extid("test", [b"abc123"]) == extids
+        assert (
+            swh_storage.extid_get_from_target(target.object_type, [target.object_id])
+            == extids
+        )
+
+        # check ExtIDs have been added to the journal
+        extids_in_journal = [
+            obj
+            for (obj_type, obj) in swh_storage.journal_writer.journal.objects
+            if obj_type == "extid"
+        ]
+        assert extids == extids_in_journal
+
     def test_release_add(self, swh_storage, sample_data):
         release, release2 = sample_data.releases[:2]