diff --git a/src/common/config_opts.h b/src/common/config_opts.h
index 0ca70dcfd5eef9..75f18aa6d5c8d2 100644
--- a/src/common/config_opts.h
+++ b/src/common/config_opts.h
@@ -483,6 +483,7 @@ OPTION(mds_bal_merge_rd, OPT_FLOAT, 1000)
 OPTION(mds_bal_merge_wr, OPT_FLOAT, 1000)
 OPTION(mds_bal_interval, OPT_INT, 10)           // seconds
 OPTION(mds_bal_fragment_interval, OPT_INT, 5)      // seconds
+OPTION(mds_bal_fragment_size_max, OPT_INT, 10000*10) // order of magnitude higher than split size
 OPTION(mds_bal_idle_threshold, OPT_FLOAT, 0)
 OPTION(mds_bal_max, OPT_INT, -1)
 OPTION(mds_bal_max_until, OPT_INT, -1)
diff --git a/src/mds/MDCache.cc b/src/mds/MDCache.cc
index f4e122505f2124..df126d6aca94c4 100644
--- a/src/mds/MDCache.cc
+++ b/src/mds/MDCache.cc
@@ -720,7 +720,7 @@ void MDCache::open_foreign_mdsdir(inodeno_t ino, MDSInternalContextBase *fin)
   discover_base_ino(ino, fin, mds_rank_t(ino & (MAX_MDS-1)));
 }
 
-CDentry *MDCache::get_or_create_stray_dentry(CInode *in)
+CDir *MDCache::get_stray_dir(CInode *in)
 {
   string straydname;
   in->name_stray_dentry(straydname);
@@ -730,6 +730,14 @@ CDentry *MDCache::get_or_create_stray_dentry(CInode *in)
   frag_t fg = strayi->pick_dirfrag(straydname);
   CDir *straydir = strayi->get_dirfrag(fg);
   assert(straydir);
+  return straydir;
+}
+
+CDentry *MDCache::get_or_create_stray_dentry(CInode *in)
+{
+  CDir *straydir = get_stray_dir(in);
+  string straydname;
+  in->name_stray_dentry(straydname);
   CDentry *straydn = straydir->lookup(straydname);
   if (!straydn) {
     straydn = straydir->add_null_dentry(straydname);
diff --git a/src/mds/MDCache.h b/src/mds/MDCache.h
index c93b7f4c4ff0fc..9152c906985445 100644
--- a/src/mds/MDCache.h
+++ b/src/mds/MDCache.h
@@ -836,6 +836,7 @@ class MDCache {
                                   version_t dpv, MDSInternalContextBase *fin);
 
   void open_foreign_mdsdir(inodeno_t ino, MDSInternalContextBase *c);
+  CDir *get_stray_dir(CInode *in);
   CDentry *get_or_create_stray_dentry(CInode *in);
 
   MDSInternalContextBase *_get_waiter(MDRequestRef& mdr, Message *req, MDSInternalContextBase *fin);
diff --git a/src/mds/Server.cc b/src/mds/Server.cc
index 11bda3adef701e..48529c7029d507 100644
--- a/src/mds/Server.cc
+++ b/src/mds/Server.cc
@@ -2149,6 +2149,23 @@ bool Server::check_access(MDRequestRef& mdr, CInode *in, unsigned mask)
   return true;
 }
 
+/**
+ * check whether fragment has reached maximum size
+ *
+ */
+bool Server::check_fragment_space(MDRequestRef &mdr, CDir *in)
+{
+  const auto size = in->get_frag_size();
+  if (size >= g_conf->mds_bal_fragment_size_max) {
+    dout(10) << "fragment " << *in << " size exceeds " << g_conf->mds_bal_fragment_size_max << " (ENOSPC)" << dendl;
+    respond_to_request(mdr, -ENOSPC);
+    return false;
+  }
+
+  return true;
+}
+
+
 /** validate_dentry_dir
  *
  * verify that the dir exists and would own the dname.
@@ -2233,15 +2250,20 @@ CDentry* Server::prepare_stray_dentry(MDRequestRef& mdr, CInode *in)
 {
   CDentry *straydn = mdr->straydn;
   if (straydn) {
-    string name;
-    in->name_stray_dentry(name);
-    if (straydn->get_name() == name)
+    string straydname;
+    in->name_stray_dentry(straydname);
+    if (straydn->get_name() == straydname)
       return straydn;
 
     assert(!mdr->done_locking);
     mdr->unpin(straydn);
   }
 
+  CDir *straydir = mdcache->get_stray_dir(in);
+
+  if (!check_fragment_space(mdr, straydir))
+    return NULL;
+
   straydn = mdcache->get_or_create_stray_dentry(in);
   mdr->straydn = straydn;
   mdr->pin(straydn);
@@ -3181,7 +3203,8 @@ void Server::handle_client_openc(MDRequestRef& mdr)
     return;
   }
 
-  CInode *diri = dn->get_dir()->get_inode();
+  CDir *dir = dn->get_dir();
+  CInode *diri = dir->get_inode();
   rdlocks.insert(&diri->authlock);
   if (!mds->locker->acquire_locks(mdr, rdlocks, wrlocks, xlocks))
     return;
@@ -3189,6 +3212,9 @@ void Server::handle_client_openc(MDRequestRef& mdr)
   if (!check_access(mdr, diri, access))
     return;
 
+  if (!check_fragment_space(mdr, dir))
+    return;
+
   CDentry::linkage_t *dnl = dn->get_projected_linkage();
 
   if (!dnl->is_null()) {
@@ -4590,6 +4616,9 @@ void Server::handle_client_mknod(MDRequestRef& mdr)
   if (!check_access(mdr, diri, MAY_WRITE))
     return;
 
+  if (!check_fragment_space(mdr, dn->get_dir()))
+    return;
+
   unsigned mode = req->head.args.mknod.mode;
   if ((mode & S_IFMT) == 0)
     mode |= S_IFREG;
@@ -4673,7 +4702,8 @@ void Server::handle_client_mkdir(MDRequestRef& mdr)
     respond_to_request(mdr, -EROFS);
     return;
   }
-  CInode *diri = dn->get_dir()->get_inode();
+  CDir *dir = dn->get_dir();
+  CInode *diri = dir->get_inode();
   rdlocks.insert(&diri->authlock);
   if (!mds->locker->acquire_locks(mdr, rdlocks, wrlocks, xlocks))
     return;
@@ -4682,6 +4712,9 @@ void Server::handle_client_mkdir(MDRequestRef& mdr)
   if (!check_access(mdr, diri, MAY_WRITE))
     return;
 
+  if (!check_fragment_space(mdr, dir))
+    return;
+
   // new inode
   SnapRealm *realm = dn->get_dir()->inode->find_snaprealm();
   snapid_t follows = realm->get_newest_seq();
@@ -4753,7 +4786,8 @@ void Server::handle_client_symlink(MDRequestRef& mdr)
     respond_to_request(mdr, -EROFS);
     return;
   }
-  CInode *diri = dn->get_dir()->get_inode();
+  CDir *dir = dn->get_dir();
+  CInode *diri = dir->get_inode();
   rdlocks.insert(&diri->authlock);
   if (!mds->locker->acquire_locks(mdr, rdlocks, wrlocks, xlocks))
     return;
@@ -4761,6 +4795,9 @@ void Server::handle_client_symlink(MDRequestRef& mdr)
   if (!check_access(mdr, diri, MAY_WRITE))
    return;
 
+  if (!check_fragment_space(mdr, dir))
+    return;
+
   unsigned mode = S_IFLNK | 0777;
   CInode *newi = prepare_new_inode(mdr, dn->get_dir(), inodeno_t(req->head.ino), mode);
   assert(newi);
@@ -4834,6 +4871,9 @@ void Server::handle_client_link(MDRequestRef& mdr)
   if (!check_access(mdr, dir->get_inode(), MAY_WRITE))
     return;
 
+  if (!check_fragment_space(mdr, dir))
+    return;
+
   // go!
   assert(g_conf->mds_kill_link_at != 1);
 
@@ -5405,6 +5445,8 @@ void Server::handle_client_unlink(MDRequestRef& mdr)
   CDentry *straydn = NULL;
   if (dnl->is_primary()) {
     straydn = prepare_stray_dentry(mdr, dnl->get_inode());
+    if (!straydn)
+      return;
     dout(10) << " straydn is " << *straydn << dendl;
   } else if (mdr->straydn) {
     mdr->unpin(mdr->straydn);
@@ -6185,6 +6227,8 @@ void Server::handle_client_rename(MDRequestRef& mdr)
   CDentry *straydn = NULL;
   if (destdnl->is_primary() && !linkmerge) {
     straydn = prepare_stray_dentry(mdr, destdnl->get_inode());
+    if (!straydn)
+      return;
     dout(10) << " straydn is " << *straydn << dendl;
   } else if (mdr->straydn) {
     mdr->unpin(mdr->straydn);
@@ -6295,6 +6339,9 @@ void Server::handle_client_rename(MDRequestRef& mdr)
   if (!check_access(mdr, destdn->get_dir()->get_inode(), MAY_WRITE))
     return;
 
+  if (!check_fragment_space(mdr, destdn->get_dir()))
+    return;
+
   if (!check_access(mdr, srci, MAY_WRITE))
     return;
 
diff --git a/src/mds/Server.h b/src/mds/Server.h
index 66aa6b9e4449de..0e871031cd2f00 100644
--- a/src/mds/Server.h
+++ b/src/mds/Server.h
@@ -134,6 +134,7 @@ class Server {
   void handle_slave_auth_pin_ack(MDRequestRef& mdr, MMDSSlaveRequest *ack);
 
   // some helpers
+  bool check_fragment_space(MDRequestRef& mdr, CDir *in);
   bool check_access(MDRequestRef& mdr, CInode *in, unsigned mask);
   bool _check_access(Session *session, CInode *in, unsigned mask, int caller_uid, int caller_gid, int setattr_uid, int setattr_gid);
   CDir *validate_dentry_dir(MDRequestRef& mdr, CInode *diri, const string& dname);