diff --git a/Program.cs b/Program.cs
index 96a59f6..caa80f4 100644
--- a/Program.cs
+++ b/Program.cs
@@ -5,6 +5,7 @@ global using DTLib.Filesystem;
 global using File = DTLib.Filesystem.File;
 global using Directory = DTLib.Filesystem.Directory;
 using DTLib.Ben.Demystifier;
+using DTLib.Extensions;
 using SyncDirectory.Storage;
 
 Console.InputEncoding = Encoding.UTF8;
@@ -18,7 +19,10 @@ try
         "SyncDirectory-data-debug"
 #endif
     );
-    storage.CreateSnapshot("tmp", "tmp");
+    var s1=storage.CreateSnapshot("tmp", "tmp");
+    var s2=storage.CreateSnapshot("tmp2", "tmp2");
+    var diff = DirectorySnapshotDiff.Diff(s1, s2);
+    Console.WriteLine(diff.FileDiffs.MergeToString('\n'));
 }
 catch (Exception ex)
 {
diff --git a/Storage/DirectorySnapshot.cs b/Storage/DirectorySnapshot.cs
index f22b4b7..0056b8a 100644
--- a/Storage/DirectorySnapshot.cs
+++ b/Storage/DirectorySnapshot.cs
@@ -1,4 +1,5 @@
-using System.Collections.Immutable;
+using System.Collections;
+using System.Collections.Immutable;
 using System.Globalization;
 using System.Linq;
 using DTLib;
@@ -10,8 +11,11 @@ public record DirectorySnapshot(
     string Name,
     IOPath Path,
     DateTime SnapshotTimeUTC,
-    IReadOnlyCollection<FileSnapshot> Files)
+    FileSnapshot[] Files)
 {
+    public Lazy<Dictionary<string, FileSnapshot>> PathMap = new(() =>
+        new Dictionary<string, FileSnapshot>(Files.ToDictionary(f=>f.Path.Str)));
+    
     public static DirectorySnapshot Parse(DtsodV23 dtsod) =>
         new DirectorySnapshot(
             dtsod["name"],
@@ -22,7 +26,7 @@ public record DirectorySnapshot(
                     CultureInfo.InvariantCulture),
             ((List<object>)dtsod["files"])
                     .Select(fd=>FileSnapshot.Parse((DtsodV23)fd))
-                    .ToImmutableList()
+                    .ToArray()
         );
     
     public DtsodV23 ToDtsod() =>
@@ -38,10 +42,7 @@ public record DirectorySnapshot(
     {
         var fileSnapshots = new List<FileSnapshot>();
         foreach (var filePath in Directory.GetAllFiles(dirPath))
-        {
-            fileSnapshots.Add(FileSnapshot.Create(filePath));
-        }
-
-        return new DirectorySnapshot(name, dirPath, DateTime.UtcNow, fileSnapshots);
+            fileSnapshots.Add(FileSnapshot.Create(filePath, dirPath));
+        return new DirectorySnapshot(name, dirPath, DateTime.UtcNow, fileSnapshots.ToArray());
     }
 }
\ No newline at end of file
diff --git a/Storage/DirectorySnapshotDiff.cs b/Storage/DirectorySnapshotDiff.cs
new file mode 100644
index 0000000..f166aed
--- /dev/null
+++ b/Storage/DirectorySnapshotDiff.cs
@@ -0,0 +1,28 @@
+using System.Linq;
+
+namespace SyncDirectory.Storage;
+
+public record DirectorySnapshotDiff(ICollection<FileSnapshotDiff> FileDiffs)
+{
+    public static DirectorySnapshotDiff Diff(DirectorySnapshot firstLocal, DirectorySnapshot secondLocal)
+    {
+        List<FileSnapshotDiff> files = new();
+        foreach (var file in secondLocal.Files)
+        {
+            if(firstLocal.PathMap.Value.TryGetValue(file.Path.Str, out var filePrev))
+            {
+                files.Add(new FileSnapshotDiff(file,
+                    file.ModifyTimeUTC == filePrev.ModifyTimeUTC ? FileStatus.Unchanged : FileStatus.Modified));
+            }
+            else  files.Add(new FileSnapshotDiff(file, FileStatus.Created));
+        }
+
+        foreach (var filePrev in firstLocal.Files)
+        {
+            if(!secondLocal.PathMap.Value.ContainsKey(filePrev.Path.Str))
+                files.Add(new FileSnapshotDiff(filePrev, FileStatus.Deleted));
+        }
+
+        return new DirectorySnapshotDiff(files);
+    }
+}
\ No newline at end of file
diff --git a/Storage/FileSnapshot.cs b/Storage/FileSnapshot.cs
index 67e3910..e4d0284 100644
--- a/Storage/FileSnapshot.cs
+++ b/Storage/FileSnapshot.cs
@@ -10,13 +10,19 @@ public record FileSnapshot(
     DateTime ModifyTimeUTC,
     DateTime SnapshotTimeUTC)
 {
-    public static FileSnapshot Create(IOPath filePath)
+    /// <summary>
+    /// Creates new FileSnapshot from an exnsting file
+    /// </summary>
+    /// <param name="fullFilePath">baseDirPath+filePathInBaseDir</param>
+    /// <param name="baseDirPath">will be removed from fullFilePath in the rezult FileSnapshot.Path</param>
+    /// <returns></returns>
+    public static FileSnapshot Create(IOPath fullFilePath, IOPath baseDirPath)
     {
-        var creationTime = System.IO.File.GetCreationTimeUtc(filePath.Str);
-        var modifyTime = System.IO.File.GetLastWriteTimeUtc(filePath.Str);
+        var creationTime = System.IO.File.GetCreationTimeUtc(fullFilePath.Str);
+        var modifyTime = System.IO.File.GetLastWriteTimeUtc(fullFilePath.Str);
         // sometimes LastWriteTime can be less then CreationTime when unpacking archives
         var latest = modifyTime > creationTime ? modifyTime : creationTime;
-        return new FileSnapshot(filePath, FileSize.Get(filePath), latest, DateTime.UtcNow);
+        return new FileSnapshot(fullFilePath.RemoveBase(baseDirPath), FileSize.Get(fullFilePath), latest, DateTime.UtcNow);
     }
 
     public static FileSnapshot Parse(DtsodV23 dtsod) =>
diff --git a/Storage/FileSnapshotDiff.cs b/Storage/FileSnapshotDiff.cs
new file mode 100644
index 0000000..3e8f840
--- /dev/null
+++ b/Storage/FileSnapshotDiff.cs
@@ -0,0 +1,6 @@
+namespace SyncDirectory.Storage;
+
+public record FileSnapshotDiff(FileSnapshot File, FileStatus Status)
+{
+    
+}
\ No newline at end of file
diff --git a/Storage/FileStatus.cs b/Storage/FileStatus.cs
new file mode 100644
index 0000000..bedc08f
--- /dev/null
+++ b/Storage/FileStatus.cs
@@ -0,0 +1,9 @@
+namespace SyncDirectory.Storage;
+
+public enum FileStatus
+{
+    Unchanged,
+    Created,
+    Modified,
+    Deleted,
+}
\ No newline at end of file