diff --git a/source/adios2/CMakeLists.txt b/source/adios2/CMakeLists.txt
index aa203a7582..5168f47fc3 100644
--- a/source/adios2/CMakeLists.txt
+++ b/source/adios2/CMakeLists.txt
@@ -56,7 +56,7 @@ add_library(adios2_core
   toolkit/format/buffer/Buffer.cpp
   toolkit/format/buffer/BufferV.cpp
   toolkit/format/buffer/malloc/MallocV.cpp
-#  toolkit/format/buffer/chunk/ChunkV.cpp
+  toolkit/format/buffer/chunk/ChunkV.cpp
   toolkit/format/buffer/heap/BufferSTL.cpp
 
   toolkit/format/bp/BPBase.cpp toolkit/format/bp/BPBase.tcc
diff --git a/source/adios2/common/ADIOSTypes.h b/source/adios2/common/ADIOSTypes.h
index 6317daff36..25f4a28473 100644
--- a/source/adios2/common/ADIOSTypes.h
+++ b/source/adios2/common/ADIOSTypes.h
@@ -185,8 +185,12 @@ constexpr uint64_t DefaultMaxBufferSize = MaxSizeT - 1;
 constexpr float DefaultBufferGrowthFactor = 1.05f;
 
 /** default Buffer Chunk Size
- *  2Gb - 100Kb (tolerance)*/
-constexpr uint64_t DefaultBufferChunkSize = 2147381248;
+ *  16Mb */
+constexpr uint64_t DefaultBufferChunkSize = 16 * 1024 * 1024;
+
+/** default minimum size not copying deferred writes
+ *  4Mb */
+constexpr size_t DefaultMinDeferredSize = 4 * 1024 * 1024;
 
 /** default size for writing/reading files using POSIX/fstream/stdio write
  *  2Gb - 100Kb (tolerance)*/
diff --git a/source/adios2/engine/bp5/BP5Engine.cpp b/source/adios2/engine/bp5/BP5Engine.cpp
index 0c8c4c635f..c2ac897c36 100644
--- a/source/adios2/engine/bp5/BP5Engine.cpp
+++ b/source/adios2/engine/bp5/BP5Engine.cpp
@@ -237,6 +237,32 @@ void BP5Engine::ParseParams(IO &io, struct BP5Params &Params)
         return false;
     };
 
+    auto lf_SetBufferVTypeParameter = [&](const std::string key, int &parameter,
+                                          int def) {
+        auto itKey = io.m_Parameters.find(key);
+        parameter = def;
+        if (itKey != io.m_Parameters.end())
+        {
+            std::string value = itKey->second;
+            std::transform(value.begin(), value.end(), value.begin(),
+                           ::tolower);
+            if (value == "malloc")
+            {
+                parameter = (int)BufferVType::MallocVType;
+            }
+            else if (value == "chunk")
+            {
+                parameter = (int)BufferVType::ChunkVType;
+            }
+            else
+            {
+                throw std::invalid_argument(
+                    "ERROR: Unknown BP5 BufferVType parameter \"" + value +
+                    "\" (must be \"malloc\" or \"chunk\"");
+            }
+        }
+    };
+
 #define get_params(Param, Type, Typedecl, Default)                             \
     lf_Set##Type##Parameter(#Param, Params.Param, Default);
     BP5_FOREACH_PARAMETER_TYPE_4ARGS(get_params);
diff --git a/source/adios2/engine/bp5/BP5Engine.h b/source/adios2/engine/bp5/BP5Engine.h
index fb00fd1121..609197f5c4 100644
--- a/source/adios2/engine/bp5/BP5Engine.h
+++ b/source/adios2/engine/bp5/BP5Engine.h
@@ -84,6 +84,15 @@ class BP5Engine
 
     std::string GetBPVersionFileName(const std::string &name) const noexcept;
 
+    enum class BufferVType
+    {
+        MallocVType,
+        ChunkVType,
+        Auto
+    };
+
+    BufferVType UseBufferV = BufferVType::ChunkVType;
+
 #define BP5_FOREACH_PARAMETER_TYPE_4ARGS(MACRO)                                \
     MACRO(OpenTimeoutSecs, Int, int, 3600)                                     \
     MACRO(BeginStepPollingFrequencySecs, Int, int, 0)                          \
@@ -97,7 +106,9 @@ class BP5Engine
     MACRO(AsyncTasks, Bool, bool, true)                                        \
     MACRO(GrowthFactor, Float, float, DefaultBufferGrowthFactor)               \
     MACRO(InitialBufferSize, SizeBytes, size_t, DefaultInitialBufferSize)      \
+    MACRO(MinDeferredSize, SizeBytes, size_t, DefaultMinDeferredSize)          \
     MACRO(BufferChunkSize, SizeBytes, size_t, DefaultBufferChunkSize)          \
+    MACRO(BufferVType, BufferVType, int, (int)BufferVType::ChunkVType)         \
     MACRO(ReaderShortCircuitReads, Bool, bool, false)
 
     struct BP5Params
diff --git a/source/adios2/engine/bp5/BP5Writer.cpp b/source/adios2/engine/bp5/BP5Writer.cpp
index 594d4a47a0..aab245698c 100644
--- a/source/adios2/engine/bp5/BP5Writer.cpp
+++ b/source/adios2/engine/bp5/BP5Writer.cpp
@@ -12,6 +12,7 @@
 #include "adios2/common/ADIOSMacros.h"
 #include "adios2/core/IO.h"
 #include "adios2/helper/adiosFunctions.h" //CheckIndexRange
+#include "adios2/toolkit/format/buffer/chunk/ChunkV.h"
 #include "adios2/toolkit/format/buffer/malloc/MallocV.h"
 #include "adios2/toolkit/transport/file/FileFStream.h"
 #include <adios2-perfstubs-interface.h>
@@ -44,9 +45,17 @@ BP5Writer::BP5Writer(IO &io, const std::string &name, const Mode mode,
 StepStatus BP5Writer::BeginStep(StepMode mode, const float timeoutSeconds)
 {
     m_WriterStep++;
-    m_BP5Serializer.InitStep(new MallocV("BP5Writer", false,
-                                         m_Parameters.InitialBufferSize,
-                                         m_Parameters.GrowthFactor));
+    if (m_Parameters.BufferVType == (int)BufferVType::MallocVType)
+    {
+        m_BP5Serializer.InitStep(new MallocV("BP5Writer", false,
+                                             m_Parameters.InitialBufferSize,
+                                             m_Parameters.GrowthFactor));
+    }
+    else
+    {
+        m_BP5Serializer.InitStep(new ChunkV("BP5Writer", true /* always copy */,
+                                            m_Parameters.BufferChunkSize));
+    }
     return StepStatus::OK;
 }
 
diff --git a/source/adios2/engine/bp5/BP5Writer.tcc b/source/adios2/engine/bp5/BP5Writer.tcc
index cd0169ffaf..5adf31ac66 100644
--- a/source/adios2/engine/bp5/BP5Writer.tcc
+++ b/source/adios2/engine/bp5/BP5Writer.tcc
@@ -48,7 +48,7 @@ void BP5Writer::PutCommon(Variable<T> &variable, const T *values, bool sync)
         /* If arrays is small, force copying to internal buffer to aggregate
          * small writes */
         size_t n = helper::GetTotalSize(variable.m_Count) * sizeof(T);
-        if (n < 4194304 /* 4MB */)
+        if (n < m_Parameters.MinDeferredSize)
         {
             sync = true;
         }
diff --git a/source/adios2/toolkit/format/buffer/chunk/ChunkV.cpp b/source/adios2/toolkit/format/buffer/chunk/ChunkV.cpp
new file mode 100644
index 0000000000..30f3615460
--- /dev/null
+++ b/source/adios2/toolkit/format/buffer/chunk/ChunkV.cpp
@@ -0,0 +1,108 @@
+/*
+ * Distributed under the OSI-approved Apache License, Version 2.0.  See
+ * accompanying file Copyright.txt for details.
+ *
+ * BufferV.cpp
+ *
+ */
+
+#include "ChunkV.h"
+#include "adios2/toolkit/format/buffer/BufferV.h"
+#include <iostream>
+#include <string.h>
+
+namespace adios2
+{
+namespace format
+{
+
+ChunkV::ChunkV(const std::string type, const bool AlwaysCopy,
+               const size_t ChunkSize)
+: BufferV(type, AlwaysCopy), m_ChunkSize(ChunkSize)
+{
+}
+
+ChunkV::~ChunkV()
+{
+    for (const auto &Chunk : m_Chunks)
+    {
+        free((void *)Chunk);
+    }
+}
+
+size_t ChunkV::AddToVec(const size_t size, const void *buf, int align,
+                        bool CopyReqd)
+{
+    int badAlign = CurOffset % align;
+    if (badAlign)
+    {
+        int addAlign = align - badAlign;
+        char zero[16] = {0};
+        AddToVec(addAlign, zero, 1, true);
+    }
+    size_t retOffset = CurOffset;
+
+    if (size == 0)
+        return CurOffset;
+
+    if (!CopyReqd && !m_AlwaysCopy)
+    {
+        // just add buf to internal version of output vector
+        VecEntry entry = {true, buf, 0, size};
+        DataV.push_back(entry);
+    }
+    else
+    {
+        // we can possibly append this entry to the last if the last was
+        // internal
+        bool AppendPossible = DataV.size() && !DataV.back().External;
+
+        if (AppendPossible && (m_TailChunkPos + size > m_ChunkSize))
+        {
+            // No room in current chunk, close it out
+            // realloc down to used size (helpful?) and set size in array
+            m_Chunks.back() = (char *)realloc(m_Chunks.back(), m_TailChunkPos);
+
+            m_TailChunkPos = 0;
+            m_TailChunk = NULL;
+            AppendPossible = false;
+        }
+        if (AppendPossible)
+        {
+            // We can use current chunk, just append the data;
+            memcpy(m_TailChunk + m_TailChunkPos, buf, size);
+            DataV.back().Size += size;
+            m_TailChunkPos += size;
+        }
+        else
+        {
+            // We need a new chunk, get the larger of size or m_ChunkSize
+            size_t NewSize = m_ChunkSize;
+            if (size > m_ChunkSize)
+                NewSize = size;
+            m_TailChunk = (char *)malloc(NewSize);
+            memcpy(m_TailChunk, buf, size);
+            m_TailChunkPos = size;
+            VecEntry entry = {false, m_TailChunk, 0, size};
+            DataV.push_back(entry);
+        }
+    }
+    CurOffset = retOffset + size;
+    return retOffset;
+}
+
+ChunkV::BufferV_iovec ChunkV::DataVec() noexcept
+{
+    BufferV_iovec ret = new iovec[DataV.size() + 1];
+    for (std::size_t i = 0; i < DataV.size(); ++i)
+    {
+        // For ChunkV, all entries in DataV are actual iov entries.
+        ret[i].iov_base = DataV[i].Base;
+        ret[i].iov_len = DataV[i].Size;
+    }
+    ret[DataV.size()] = {NULL, 0};
+    return ret;
+}
+
+} // end namespace format
+} // end namespace adios2
diff --git a/source/adios2/toolkit/format/buffer/chunk/ChunkV.h b/source/adios2/toolkit/format/buffer/chunk/ChunkV.h
new file mode 100644
index 0000000000..c0eb02a8bf
--- /dev/null
+++ b/source/adios2/toolkit/format/buffer/chunk/ChunkV.h
@@ -0,0 +1,45 @@
+/*
+ * Distributed under the OSI-approved Apache License, Version 2.0.  See
+ * accompanying file Copyright.txt for details.
+ *
+ */
+
+#ifndef ADIOS2_TOOLKIT_FORMAT_BUFFER_MALLOC_CHUNKV_H_
+#define ADIOS2_TOOLKIT_FORMAT_BUFFER_MALLOC_CHUNKV_H_
+
+#include "adios2/common/ADIOSConfig.h"
+#include "adios2/common/ADIOSTypes.h"
+
+#include "adios2/toolkit/format/buffer/BufferV.h"
+
+namespace adios2
+{
+namespace format
+{
+
+class ChunkV : public BufferV
+{
+public:
+    uint64_t Size() noexcept;
+
+    const size_t m_ChunkSize;
+
+    ChunkV(const std::string type, const bool AlwaysCopy = false,
+           const size_t ChunkSize = DefaultBufferChunkSize);
+    virtual ~ChunkV();
+
+    virtual BufferV_iovec DataVec() noexcept;
+
+    virtual size_t AddToVec(const size_t size, const void *buf, int align,
+                            bool CopyReqd);
+
+private:
+    std::vector<char *> m_Chunks;
+    size_t m_TailChunkPos = 0;
+    char *m_TailChunk = NULL;
+};
+
+} // end namespace format
+} // end namespace adios2
+
+#endif /* ADIOS2_TOOLKIT_FORMAT_BUFFER_MALLOC_MALLOCV_H_ */