diff --git a/thorlcr/msort/tsorts.cpp b/thorlcr/msort/tsorts.cpp
index f2603ea7c45..5f4533de69d 100644
--- a/thorlcr/msort/tsorts.cpp
+++ b/thorlcr/msort/tsorts.cpp
@@ -69,7 +69,7 @@ class CWriteIntercept : public CSimpleInterface
     CActivityBase &activity;
     CriticalSection crit;
     IThorRowInterfaces *rowIf;
-    Owned<IFile> dataFile, idxFile;
+    Owned<CFileOwner> dataFile, idxFile;
     Owned<IFileIO> dataFileIO, idxFileIO;
     Owned<ISerialStream> dataFileStream;
     Linked<IFileIOStream> idxFileStream;
@@ -91,6 +91,7 @@ class CWriteIntercept : public CSimpleInterface
         if (idxFileStream.get())
         {
             idxFileStream->write(sizeof(o),&o);
+            idxFile->noteSize(idxFileIO->getStatistic(StSizeDiskWrite));
             return;
         }
         if (lastofs)
@@ -100,12 +101,13 @@ class CWriteIntercept : public CSimpleInterface
                 // right create idx
                 StringBuffer tempname;
                 GetTempFilePath(tempname.clear(),"srtidx");
-                idxFile.setown(createIFile(tempname.str()));
-                idxFileIO.setown(idxFile->open(IFOcreaterw));
+                Owned<IFile> tmpFile = createIFile(tempname.str());
+                idxFile.setown(new CFileOwner(tmpFile, activity.queryTempFileSizeTracker()));
+                idxFileIO.setown(tmpFile->open(IFOcreaterw));
                 if (!idxFileIO.get())
                 {
                     StringBuffer err;
-                    err.append("Cannot create ").append(idxFile->queryFilename());
+                    err.append("Cannot create ").append(tmpFile->queryFilename());
                     LOG(MCerror, "%s", err.str());
                     throw MakeActivityException(&activity, -1, "%s", err.str());
                 }
@@ -141,7 +143,7 @@ class CWriteIntercept : public CSimpleInterface
         if (!idxFileIO.get())
         {
             assertex(idxFile);
-            idxFileIO.setown(idxFile->open(IFOread));
+            idxFileIO.setown(idxFile->queryIFile().open(IFOread));
         }
         size32_t rd = idxFileIO->read((offset_t)pos*(offset_t)sizeof(offset_t),sizeof(*ofs)*n,ofs);
         if (closeIO)
@@ -161,12 +163,12 @@ class CWriteIntercept : public CSimpleInterface
         {
             if (parent->compressedOverflowFile)
             {
-                Owned<ICompressedFileIO> iFileIO = createCompressedFileReader(parent->dataFile);
+                Owned<ICompressedFileIO> iFileIO = createCompressedFileReader(&(parent->dataFile->queryIFile()));
                 assertex(iFileIO);
                 stream.setown(createRowStreamEx(iFileIO, parent->rowIf, startOffset, (offset_t)-1, max));
             }
             else
-                stream.setown(createRowStreamEx(parent->dataFile, parent->rowIf, startOffset, (offset_t)-1, max));
+                stream.setown(createRowStreamEx(&(parent->dataFile->queryIFile()), parent->rowIf, startOffset, (offset_t)-1, max));
         }
         virtual const void *nextRow() { return stream->nextRow(); }
         virtual void stop() { stream->stop(); }
@@ -187,16 +189,13 @@ class CWriteIntercept : public CSimpleInterface
     ~CWriteIntercept()
     {
         closeFiles();
-        if (dataFile)
-            dataFile->remove();
-        if (idxFile)
-            idxFile->remove();
     }
     offset_t write(IRowStream *input)
     {
         StringBuffer tempname;
         GetTempFilePath(tempname,"srtmrg");
-        dataFile.setown(createIFile(tempname.str()));
+        Owned<IFile> tmpFile = createIFile(tempname.str());
+        dataFile.setown(new CFileOwner(tmpFile, activity.queryTempFileSizeTracker()));
 
         unsigned rwFlags = DEFAULT_RWFLAGS;
         size32_t compBlkSz = 0;
@@ -227,7 +226,7 @@ class CWriteIntercept : public CSimpleInterface
             }
         }
 
-        Owned<IExtRowWriter> output = createRowWriter(dataFile, rowIf, rwFlags, nullptr, compBlkSz);
+        Owned<IExtRowWriter> output = createRowWriter(&(dataFile->queryIFile()), rowIf, rwFlags, nullptr, compBlkSz);
 
         bool overflowed = false;
         ActPrintLog(&activity, "Local Overflow Merge start");
@@ -262,6 +261,7 @@ class CWriteIntercept : public CSimpleInterface
         output->flush();
         offset_t end = output->getPosition();
         output.clear();
+        dataFile->noteSize(dataFileIO->getStatistic(StSizeDiskWrite));
         writeidxofs(end);
         if (idxFileIO)
         {
@@ -271,7 +271,7 @@ class CWriteIntercept : public CSimpleInterface
         }
         if (overflowed)
             IWARNLOG("Overflowed by %" I64F "d", overflowsize);
-        ActPrintLog(&activity, "Local Overflow Merge done: overflow file '%s', size = %" I64F "d", dataFile->queryFilename(), dataFile->size());
+        ActPrintLog(&activity, "Local Overflow Merge done: overflow file '%s', size = %" I64F "d", dataFile->queryIFile().queryFilename(), dataFile->queryIFile().size());
         return end;
     }
     IRowStream *getStream(offset_t startOffset, rowcount_t max)
@@ -299,7 +299,7 @@ class CWriteIntercept : public CSimpleInterface
         size32_t idxSz = (size32_t)(ofs[1]-ofs[0]);
         if (!dataFileIO)
         {
-            dataFileIO.setown(dataFile->open(IFOread));
+            dataFileIO.setown(dataFile->queryIFile().open(IFOread));
             if (compressedOverflowFile)
             {
                 dataFileIO.setown(createCompressedFileReader(dataFileIO));
diff --git a/thorlcr/thorutil/thmem.cpp b/thorlcr/thorutil/thmem.cpp
index d866d39a564..f2dbe309d6e 100644
--- a/thorlcr/thorutil/thmem.cpp
+++ b/thorlcr/thorutil/thmem.cpp
@@ -246,7 +246,7 @@ class CSpillableStreamBase : public CSpillable
         VStringBuffer tempPrefix("streamspill_%d", activity.queryId());
         GetTempFilePath(tempName, tempPrefix.str());
         OwnedIFile iFile = createIFile(tempName.str());
-        spillFile.setown(new CFileOwner(iFile.getLink(), activity.queryTempFileSizeTracker()));
+        spillFile.setown(new CFileOwner(iFile, activity.queryTempFileSizeTracker()));
 
         VStringBuffer spillPrefixStr("SpillableStream(%u)", spillPriority);
         rows.save(*iFile, spillCompInfo, false, spillPrefixStr.str()); // saves committed rows
@@ -1660,7 +1660,7 @@ class CThorRowCollectorBase : public CSpillable
         Owned<IFile> iFile = createIFile(tempName.str());
         VStringBuffer spillPrefixStr("%sRowCollector(%d)", tracingPrefix.str(), spillPriority);
         spillableRows.save(*iFile, spillCompInfo, false, spillPrefixStr.str()); // saves committed rows
-        Owned<CFileOwner> tempFileOwner = new CFileOwner(iFile.getLink(), tempFileSizeTracker);
+        Owned<CFileOwner> tempFileOwner = new CFileOwner(iFile, tempFileSizeTracker);
         spillFiles.append(tempFileOwner.getLink());
         ++overflowCount;
         statOverflowCount.fastAdd(1); // NB: this is total over multiple uses of this class
diff --git a/thorlcr/thorutil/thormisc.cpp b/thorlcr/thorutil/thormisc.cpp
index a97fc94c5f8..c6de269762e 100644
--- a/thorlcr/thorutil/thormisc.cpp
+++ b/thorlcr/thorutil/thormisc.cpp
@@ -73,7 +73,7 @@ Owned<IPropertyTree> globals;
 static Owned<IMPtagAllocator> ClusterMPAllocator;
 
 // stat. mappings shared between master and slave activities
-const StatisticsMapping spillStatistics({StTimeSpillElapsed, StTimeSortElapsed, StNumSpills, StSizeSpillFile});
+const StatisticsMapping spillStatistics({StTimeSpillElapsed, StTimeSortElapsed, StNumSpills, StSizeSpillFile, StSizePeakTempDisk});
 const StatisticsMapping soapcallStatistics({StTimeSoapcall});
 const StatisticsMapping basicActivityStatistics({StTimeTotalExecute, StTimeLocalExecute, StTimeBlocked});
 const StatisticsMapping groupActivityStatistics({StNumGroups, StNumGroupMax}, basicActivityStatistics);
diff --git a/thorlcr/thorutil/thormisc.hpp b/thorlcr/thorutil/thormisc.hpp
index 2bc8f0c776d..9faad9556ae 100644
--- a/thorlcr/thorutil/thormisc.hpp
+++ b/thorlcr/thorutil/thormisc.hpp
@@ -356,9 +356,14 @@ class graph_decl CFileOwner : public CSimpleInterface, implements IInterface
     }
     void noteSize(offset_t size)
     {
-        fileSize = size;
-        if (fileSizeTracker)
-            fileSizeTracker->growSize(fileSize);
+        if (fileSizeTracker && fileSize!=size)
+        {
+            if (size > fileSize)
+                fileSizeTracker->growSize(size-fileSize);
+            else
+                fileSizeTracker->shrinkSize(fileSize-size);
+            fileSize = size;
+        }
     }
     IFile &queryIFile() const { return *iFile; }
 };