diff --git a/include/dwarfs/inode_manager.h b/include/dwarfs/inode_manager.h
index 9e263b15..849484da 100644
--- a/include/dwarfs/inode_manager.h
+++ b/include/dwarfs/inode_manager.h
@@ -54,8 +54,9 @@ class inode_manager {
 
   size_t count() const { return impl_->count(); }
 
-  void order_inodes(std::shared_ptr<script> scr, order_cb const& fn) {
-    impl_->order_inodes(std::move(scr), fn);
+  void order_inodes(worker_group& wg, std::shared_ptr<script> scr,
+                    order_cb const& fn) {
+    impl_->order_inodes(wg, std::move(scr), fn);
   }
 
   void for_each_inode_in_order(inode_cb const& fn) const {
@@ -84,8 +85,8 @@ class inode_manager {
 
     virtual std::shared_ptr<inode> create_inode() = 0;
     virtual size_t count() const = 0;
-    virtual void
-    order_inodes(std::shared_ptr<script> scr, order_cb const& fn) = 0;
+    virtual void order_inodes(worker_group& wg, std::shared_ptr<script> scr,
+                              order_cb const& fn) = 0;
     virtual void for_each_inode_in_order(
         std::function<void(std::shared_ptr<inode> const&)> const& fn) const = 0;
     virtual std::vector<std::pair<fragment_category::value_type, size_t>>
diff --git a/include/dwarfs/options.h b/include/dwarfs/options.h
index 0ac40159..ab3e6fde 100644
--- a/include/dwarfs/options.h
+++ b/include/dwarfs/options.h
@@ -98,7 +98,14 @@ struct filesystem_writer_options {
 };
 
 // TODO: rename
-enum class file_order_mode { NONE, PATH, SCRIPT, SIMILARITY, NILSIMSA };
+enum class file_order_mode {
+  NONE,
+  PATH,
+  SCRIPT,
+  SIMILARITY,
+  NILSIMSA,
+  NILSIMSA2
+};
 
 // TODO: rename
 struct file_order_options {
@@ -106,6 +113,8 @@ struct file_order_options {
   int nilsimsa_depth{20000};
   int nilsimsa_min_depth{1000};
   int nilsimsa_limit{255};
+  int nilsimsa2_max_children{8192};
+  int nilsimsa2_max_cluster_size{8192};
 };
 
 struct inode_options {
diff --git a/src/dwarfs/fragment_order_parser.cpp b/src/dwarfs/fragment_order_parser.cpp
index f10d2c4d..07bbcb69 100644
--- a/src/dwarfs/fragment_order_parser.cpp
+++ b/src/dwarfs/fragment_order_parser.cpp
@@ -41,6 +41,7 @@ const std::map<std::string_view, file_order_mode> order_choices{
 #endif
     {"similarity", file_order_mode::SIMILARITY},
     {"nilsimsa", file_order_mode::NILSIMSA},
+    {"nilsimsa2", file_order_mode::NILSIMSA2},
 };
 
 void parse_order_option(std::string_view ordname, std::string_view opt,
@@ -96,27 +97,48 @@ file_order_options fragment_order_parser::parse(std::string_view arg) const {
     rv.mode = it->second;
 
     if (order_opts.size() > 1) {
-      if (rv.mode != file_order_mode::NILSIMSA) {
-        throw std::runtime_error(
-            fmt::format("inode order mode '{}' does not support options",
-                        order_opts.front()));
-      }
-
-      if (order_opts.size() > 4) {
-        throw std::runtime_error(fmt::format(
-            "too many options for inode order mode '{}'", order_opts.front()));
-      }
-
       auto ordname = order_opts[0];
 
-      parse_order_option(ordname, order_opts[1], rv.nilsimsa_limit, "limit", 0,
-                         255);
+      switch (rv.mode) {
+      case file_order_mode::NILSIMSA:
+        if (order_opts.size() > 4) {
+          throw std::runtime_error(fmt::format(
+              "too many options for inode order mode '{}'", ordname));
+        }
 
-      parse_order_option(ordname, order_opts[2], rv.nilsimsa_depth, "depth", 0);
+        parse_order_option(ordname, order_opts[1], rv.nilsimsa_limit, "limit",
+                           0, 255);
 
-      if (order_opts.size() > 3) {
-        parse_order_option(ordname, order_opts[3], rv.nilsimsa_min_depth,
-                           "min depth", 0);
+        if (order_opts.size() > 2) {
+          parse_order_option(ordname, order_opts[2], rv.nilsimsa_depth, "depth",
+                             0);
+
+          if (order_opts.size() > 3) {
+            parse_order_option(ordname, order_opts[3], rv.nilsimsa_min_depth,
+                               "min depth", 0);
+          }
+        }
+        break;
+
+      case file_order_mode::NILSIMSA2:
+        if (order_opts.size() > 4) {
+          throw std::runtime_error(fmt::format(
+              "too many options for inode order mode '{}'", ordname));
+        }
+
+        parse_order_option(ordname, order_opts[1], rv.nilsimsa2_max_children,
+                           "max_children", 0);
+
+        if (order_opts.size() > 2) {
+          parse_order_option(ordname, order_opts[2],
+                             rv.nilsimsa2_max_cluster_size, "max_cluster_size",
+                             0);
+        }
+        break;
+
+      default:
+        throw std::runtime_error(fmt::format(
+            "inode order mode '{}' does not support options", ordname));
       }
     }
   } else {
@@ -145,6 +167,11 @@ fragment_order_parser::to_string(file_order_options const& opts) const {
     return fmt::format("nilsimsa (limit={}, depth={}, min_depth={})",
                        opts.nilsimsa_limit, opts.nilsimsa_depth,
                        opts.nilsimsa_min_depth);
+
+  case file_order_mode::NILSIMSA2:
+    return fmt::format("nilsimsa2 (max_children={}, max_cluster_size={})",
+                       opts.nilsimsa2_max_children,
+                       opts.nilsimsa2_max_cluster_size);
   }
   return "<unknown>";
 }
diff --git a/src/dwarfs/inode_manager.cpp b/src/dwarfs/inode_manager.cpp
index 92682d11..d74589b8 100644
--- a/src/dwarfs/inode_manager.cpp
+++ b/src/dwarfs/inode_manager.cpp
@@ -54,6 +54,7 @@
 #include "dwarfs/progress.h"
 #include "dwarfs/script.h"
 #include "dwarfs/similarity.h"
+#include "dwarfs/similarity_ordering.h"
 #include "dwarfs/worker_group.h"
 
 #include "dwarfs/gen-cpp2/metadata_types.h"
@@ -336,6 +337,7 @@ class inode_ : public inode {
         sc.try_emplace(f.category());
         break;
       case file_order_mode::NILSIMSA:
+      case file_order_mode::NILSIMSA2:
         nc.try_emplace(f.category());
         break;
       }
@@ -397,7 +399,8 @@ class inode_ : public inode {
       similarity_.emplace<uint32_t>(sc.finalize());
     } break;
 
-    case file_order_mode::NILSIMSA: {
+    case file_order_mode::NILSIMSA:
+    case file_order_mode::NILSIMSA2: {
       nilsimsa nc;
       scan_range(mm, 0, mm->size(), nc);
       // TODO: can we finalize in-place?
@@ -440,6 +443,63 @@ class inode_ : public inode {
       nilsimsa_similarity_hash_; // TODO: remove (move to similarity_)
 };
 
+class inode_element_view
+    : public basic_array_similarity_element_view<256, uint64_t> {
+ public:
+  inode_element_view(std::vector<std::shared_ptr<inode>> const& inodes)
+      : inodes_{inodes} {}
+
+  bool exists(size_t /*i*/) const override {
+    // TODO: not true once we use fragments
+    return true;
+  }
+
+  size_t size() const override { return inodes_.size(); }
+
+  size_t weight(size_t i) const override { return inodes_[i]->any()->size(); }
+
+  bool bitvec_less(size_t a, size_t b) const override {
+    auto const& ia = *inodes_[a];
+    auto const& ib = *inodes_[b];
+    if (ia.nilsimsa_similarity_hash() < ib.nilsimsa_similarity_hash()) {
+      return true;
+    }
+    if (ia.nilsimsa_similarity_hash() > ib.nilsimsa_similarity_hash()) {
+      return false;
+    }
+    auto const& fa = *ia.any();
+    auto const& fb = *ib.any();
+    return fa.less_revpath(fb);
+  }
+
+  bool order_less(size_t a, size_t b) const override {
+    auto const& ia = *inodes_[a];
+    auto const& ib = *inodes_[b];
+    auto const& fa = *ia.any();
+    auto const& fb = *ib.any();
+    auto sa = fa.size();
+    auto sb = fb.size();
+    return sa > sb || (sa == sb && fa.less_revpath(fb));
+  }
+
+  bool bits_equal(size_t a, size_t b) const override {
+    return inodes_[a]->nilsimsa_similarity_hash() ==
+           inodes_[b]->nilsimsa_similarity_hash();
+  }
+
+  std::string description(size_t i) const override {
+    auto f = inodes_[i]->any();
+    return fmt::format("{} [{}]", f->path_as_string(), f->size());
+  }
+
+  nilsimsa::hash_type const& get_bits(size_t i) const override {
+    return inodes_[i]->nilsimsa_similarity_hash();
+  }
+
+ private:
+  std::vector<std::shared_ptr<inode>> const& inodes_;
+};
+
 } // namespace
 
 template <typename LoggerPolicy>
@@ -459,7 +519,7 @@ class inode_manager_ final : public inode_manager::impl {
 
   size_t count() const override { return inodes_.size(); }
 
-  void order_inodes(std::shared_ptr<script> scr,
+  void order_inodes(worker_group& wg, std::shared_ptr<script> scr,
                     inode_manager::order_cb const& fn) override;
 
   void for_each_inode_in_order(
@@ -532,7 +592,8 @@ class inode_manager_ final : public inode_manager::impl {
 
     return opts.fragment_order.any_is([](auto const& order) {
       return order.mode == file_order_mode::SIMILARITY ||
-             order.mode == file_order_mode::NILSIMSA;
+             order.mode == file_order_mode::NILSIMSA ||
+             order.mode == file_order_mode::NILSIMSA2;
     });
   }
 
@@ -578,6 +639,7 @@ class inode_manager_ final : public inode_manager::impl {
                      std::vector<uint32_t>& index);
 
   void order_inodes_by_nilsimsa(inode_manager::order_cb const& fn);
+  void order_inodes_by_nilsimsa2(worker_group& wg);
 
   LOG_PROXY_DECL(LoggerPolicy);
   std::vector<std::shared_ptr<inode>> inodes_;
@@ -617,7 +679,10 @@ void inode_manager_<LoggerPolicy>::scan_background(worker_group& wg,
 
 template <typename LoggerPolicy>
 void inode_manager_<LoggerPolicy>::order_inodes(
-    std::shared_ptr<script> scr, inode_manager::order_cb const& fn) {
+    worker_group& wg, std::shared_ptr<script> scr,
+    inode_manager::order_cb const& fn) {
+  // TODO: only use an index, never actually reorder inodes
+
   // TODO:
   switch (opts_.fragment_order.get().mode) {
   case file_order_mode::NONE:
@@ -659,6 +724,15 @@ void inode_manager_<LoggerPolicy>::order_inodes(
     ti << count() << " inodes ordered";
     return;
   }
+
+  case file_order_mode::NILSIMSA2: {
+    LOG_INFO << "ordering " << count()
+             << " inodes using new nilsimsa similarity...";
+    auto ti = LOG_CPU_TIMED_INFO;
+    order_inodes_by_nilsimsa2(wg);
+    ti << count() << " inodes ordered";
+    break;
+  }
   }
 
   LOG_INFO << "assigning file inodes...";
@@ -824,6 +898,23 @@ void inode_manager_<LoggerPolicy>::order_inodes_by_nilsimsa(
   }
 }
 
+template <typename LoggerPolicy>
+void inode_manager_<LoggerPolicy>::order_inodes_by_nilsimsa2(worker_group& wg) {
+  auto const& file_order = opts_.fragment_order.get(); // TODO
+  similarity_ordering_options opts;
+  opts.max_children = file_order.nilsimsa2_max_children;
+  opts.max_cluster_size = file_order.nilsimsa2_max_cluster_size;
+  auto sim_order = similarity_ordering(LOG_GET_LOGGER, prog_, wg, opts);
+  inode_element_view ev(inodes_);
+  auto ordered = sim_order.order_nilsimsa(ev).get();
+  std::vector<std::shared_ptr<inode>> inodes;
+  inodes.reserve(inodes_.size());
+  for (auto i : ordered) {
+    inodes.push_back(std::move(inodes_[i]));
+  }
+  inodes.swap(inodes_);
+}
+
 template <typename LoggerPolicy>
 void inode_manager_<LoggerPolicy>::dump(std::ostream& os) const {
   for_each_inode_in_order(
diff --git a/src/dwarfs/scanner.cpp b/src/dwarfs/scanner.cpp
index c854325c..d3cbc762 100644
--- a/src/dwarfs/scanner.cpp
+++ b/src/dwarfs/scanner.cpp
@@ -33,6 +33,7 @@
 #include <vector>
 
 #include <folly/ExceptionString.h>
+#include <folly/system/HardwareConcurrency.h>
 
 #include <fmt/format.h>
 
@@ -663,25 +664,28 @@ void scanner_<LoggerPolicy>::scan(
     worker_group blockify("blockify", 1, 1 << 20);
 
     {
-      worker_group ordering("ordering", 1);
+      // TODO
+      size_t const num_threads = std::max(folly::hardware_concurrency(), 1u);
+      worker_group wg_order("ordering", num_threads);
 
-      ordering.add_job([&] {
-        im.order_inodes(script_, [&](std::shared_ptr<inode> const& ino) {
-          blockify.add_job([&] {
-            prog.current.store(ino.get());
-            bm.add_inode(ino);
-            prog.inodes_written++;
-          });
-          auto queued_files = blockify.queue_size();
-          auto queued_blocks = fsw.queue_fill();
-          prog.blockify_queue = queued_files;
-          prog.compress_queue = queued_blocks;
-          return INT64_C(500) * queued_blocks +
-                 static_cast<int64_t>(queued_files);
-        });
-      });
+      // ordering.add_job([&] {
+      im.order_inodes(wg_order, script_,
+                      [&](std::shared_ptr<inode> const& ino) {
+                        blockify.add_job([&] {
+                          prog.current.store(ino.get());
+                          bm.add_inode(ino);
+                          prog.inodes_written++;
+                        });
+                        auto queued_files = blockify.queue_size();
+                        auto queued_blocks = fsw.queue_fill();
+                        prog.blockify_queue = queued_files;
+                        prog.compress_queue = queued_blocks;
+                        return INT64_C(500) * queued_blocks +
+                               static_cast<int64_t>(queued_files);
+                      });
+      // });
 
-      ordering.wait();
+      // wg_order.wait();
     }
 
     LOG_INFO << "waiting for segmenting/blockifying to finish...";
diff --git a/test/dwarfs.cpp b/test/dwarfs.cpp
index 7ec20c6f..4f170f9d 100644
--- a/test/dwarfs.cpp
+++ b/test/dwarfs.cpp
@@ -157,7 +157,8 @@ void basic_end_to_end_test(std::string const& compressor,
   auto mm = std::make_shared<test::mmap_mock>(std::move(fsimage));
 
   bool similarity = file_order == file_order_mode::SIMILARITY ||
-                    file_order == file_order_mode::NILSIMSA;
+                    file_order == file_order_mode::NILSIMSA ||
+                    file_order == file_order_mode::NILSIMSA2;
 
   size_t const num_fail_empty = access_fail ? 1 : 0;
 
@@ -599,6 +600,7 @@ INSTANTIATE_TEST_SUITE_P(
         ::testing::ValuesIn(compressions), ::testing::Values(12, 15, 20, 28),
         ::testing::Values(file_order_mode::NONE, file_order_mode::PATH,
                           file_order_mode::SCRIPT, file_order_mode::NILSIMSA,
+                          file_order_mode::NILSIMSA2,
                           file_order_mode::SIMILARITY),
         ::testing::Values(std::nullopt, "xxh3-128")));