diff --git a/backend/posix/data_io_linux.go b/backend/posix/data_io_linux.go
new file mode 100644
index 00000000..4c1b552c
--- /dev/null
+++ b/backend/posix/data_io_linux.go
@@ -0,0 +1,192 @@
+// Copyright 2026 Versity Software
+// This file is licensed under the Apache License, Version 2.0
+// (the "License"); you may not use this file except in compliance
+// with the License.  You may obtain a copy of the License at
+//
+//   http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing,
+// software distributed under the License is distributed on an
+// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+// KIND, either express or implied.  See the License for the
+// specific language governing permissions and limitations
+// under the License.
+
+//go:build linux
+
+package posix
+
+import (
+	"fmt"
+	"io"
+	"os"
+	"path/filepath"
+	"strconv"
+	"sync"
+	"syscall"
+
+	"github.com/versity/versitygw/backend"
+)
+
+// openDataRead opens object data for reading and applies O_DIRECT when
+// requested. O_DIRECT is best-effort and falls back to buffered I/O when
+// unsupported by the filesystem.
+func openDataRead(name string, useODirect bool) (*os.File, error) {
+	if !useODirect {
+		return os.Open(name)
+	}
+
+	f, err := os.OpenFile(name, syscall.O_RDONLY|syscall.O_DIRECT, 0)
+	if err != nil {
+		if isODirectUnsupportedOpenErr(err) {
+			warnODirectUnsupportedOnce("openDataRead", err)
+			return os.Open(name)
+		}
+
+		return nil, err
+	}
+
+	return f, nil
+}
+
+func buildGetObjectBody(f *os.File, path string, startOffset, length, objSize int64, useODirect bool, readBufferSize int) (io.ReadCloser, error) {
+	if startOffset == 0 && length == objSize {
+		if useODirect {
+			return newODirectReadFallbackFile(path, f, true), nil
+		}
+		return f, nil
+	}
+
+	if !useODirect {
+		rdr := io.NewSectionReader(f, startOffset, length)
+		return withReadBufferSize(&backend.FileSectionReadCloser{R: rdr, F: f}, readBufferSize), nil
+	}
+
+	rf := newODirectReadFallbackFile(path, f, true)
+
+	if _, err := rf.Seek(startOffset, io.SeekStart); err != nil {
+		_ = rf.Close()
+		return nil, fmt.Errorf("seek range start: %w", err)
+	}
+
+	return withReadBufferSize(&readerWithCloser{r: io.LimitReader(rf, length), c: rf}, readBufferSize), nil
+}
+
+type readerWithCloser struct {
+	r io.Reader
+	c io.Closer
+}
+
+func (r *readerWithCloser) Read(p []byte) (int, error) {
+	return r.r.Read(p)
+}
+
+func (r *readerWithCloser) Close() error {
+	return r.c.Close()
+}
+
+type odirectReadFallbackFile struct {
+	mu         sync.Mutex
+	path       string
+	f          *os.File
+	useODirect bool
+}
+
+func newODirectReadFallbackFile(path string, f *os.File, useODirect bool) *odirectReadFallbackFile {
+	return &odirectReadFallbackFile{
+		path:       path,
+		f:          f,
+		useODirect: useODirect,
+	}
+}
+
+func (r *odirectReadFallbackFile) Read(p []byte) (int, error) {
+	r.mu.Lock()
+	defer r.mu.Unlock()
+
+	n, err := r.f.Read(p)
+	if err != nil && n == 0 && r.useODirect && isODirectRuntimeFallbackErr(err) {
+		if fallbackErr := r.switchToBufferedAtCurrentOffsetLocked(); fallbackErr != nil {
+			return 0, fallbackErr
+		}
+
+		return r.f.Read(p)
+	}
+
+	return n, err
+}
+
+func (r *odirectReadFallbackFile) WriteTo(w io.Writer) (int64, error) {
+	r.mu.Lock()
+	useODirect := r.useODirect
+	f := r.f
+	r.mu.Unlock()
+
+	if !useODirect {
+		return io.Copy(w, &onlyRead{r})
+	}
+
+	writerTo, ok := interface{}(f).(io.WriterTo)
+	if !ok {
+		return io.Copy(w, &onlyRead{r})
+	}
+
+	n, err := writerTo.WriteTo(w)
+	if err == nil || !isODirectRuntimeFallbackErr(err) {
+		return n, err
+	}
+
+	r.mu.Lock()
+	fallbackErr := r.switchToBufferedAtCurrentOffsetLocked()
+	r.mu.Unlock()
+	if fallbackErr != nil {
+		return n, fallbackErr
+	}
+
+	m, err := io.Copy(w, &onlyRead{r})
+	return n + m, err
+}
+
+func (r *odirectReadFallbackFile) Seek(offset int64, whence int) (int64, error) {
+	r.mu.Lock()
+	defer r.mu.Unlock()
+	return r.f.Seek(offset, whence)
+}
+
+func (r *odirectReadFallbackFile) Close() error {
+	r.mu.Lock()
+	defer r.mu.Unlock()
+	return r.f.Close()
+}
+
+func (r *odirectReadFallbackFile) switchToBufferedAtOffset(offset int64) error {
+	fd := strconv.Itoa(int(r.f.Fd()))
+	bf, openErr := os.Open(filepath.Join(procfddir, fd))
+	if openErr != nil {
+		return openErr
+	}
+
+	if _, seekErr := bf.Seek(offset, io.SeekStart); seekErr != nil {
+		_ = bf.Close()
+		return seekErr
+	}
+
+	if closeErr := r.f.Close(); closeErr != nil {
+		_ = bf.Close()
+		return closeErr
+	}
+
+	r.f = bf
+	r.useODirect = false
+
+	return nil
+}
+
+func (r *odirectReadFallbackFile) switchToBufferedAtCurrentOffsetLocked() error {
+	offset, seekErr := r.f.Seek(0, io.SeekCurrent)
+	if seekErr != nil {
+		return seekErr
+	}
+
+	return r.switchToBufferedAtOffset(offset)
+}
diff --git a/backend/posix/data_io_nonlinux.go b/backend/posix/data_io_nonlinux.go
new file mode 100644
index 00000000..0cab180e
--- /dev/null
+++ b/backend/posix/data_io_nonlinux.go
@@ -0,0 +1,33 @@
+// Copyright 2026 Versity Software
+// This file is licensed under the Apache License, Version 2.0
+// (the "License"); you may not use this file except in compliance
+// with the License.  You may obtain a copy of the License at
+//
+//   http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing,
+// software distributed under the License is distributed on an
+// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+// KIND, either express or implied.  See the License for the
+// specific language governing permissions and limitations
+// under the License.
+
+//go:build !linux
+
+package posix
+
+import (
+	"io"
+	"os"
+
+	"github.com/versity/versitygw/backend"
+)
+
+func buildGetObjectBody(f *os.File, _ string, startOffset, length, objSize int64, _ bool, readBufferSize int) (io.ReadCloser, error) {
+	if startOffset == 0 && length == objSize {
+		return f, nil
+	}
+
+	rdr := io.NewSectionReader(f, startOffset, length)
+	return withReadBufferSize(&backend.FileSectionReadCloser{R: rdr, F: f}, readBufferSize), nil
+}
diff --git a/backend/posix/data_io_other.go b/backend/posix/data_io_other.go
new file mode 100644
index 00000000..790f3daa
--- /dev/null
+++ b/backend/posix/data_io_other.go
@@ -0,0 +1,26 @@
+// Copyright 2026 Versity Software
+// This file is licensed under the Apache License, Version 2.0
+// (the "License"); you may not use this file except in compliance
+// with the License.  You may obtain a copy of the License at
+//
+//   http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing,
+// software distributed under the License is distributed on an
+// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+// KIND, either express or implied.  See the License for the
+// specific language governing permissions and limitations
+// under the License.
+
+//go:build !linux && !windows
+
+package posix
+
+import "os"
+
+func openDataRead(name string, useODirect bool) (*os.File, error) {
+	if useODirect {
+		warnODirectUnsupportedOnce("openDataRead-nonlinux", os.ErrInvalid)
+	}
+	return os.Open(name)
+}
diff --git a/backend/posix/data_io_windows.go b/backend/posix/data_io_windows.go
new file mode 100644
index 00000000..eeca1070
--- /dev/null
+++ b/backend/posix/data_io_windows.go
@@ -0,0 +1,46 @@
+// Copyright 2026 Versity Software
+// This file is licensed under the Apache License, Version 2.0
+// (the "License"); you may not use this file except in compliance
+// with the License.  You may obtain a copy of the License at
+//
+//   http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing,
+// software distributed under the License is distributed on an
+// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+// KIND, either express or implied.  See the License for the
+// specific language governing permissions and limitations
+// under the License.
+
+//go:build windows
+
+package posix
+
+import (
+	"os"
+	"syscall"
+)
+
+func openDataRead(name string, useODirect bool) (*os.File, error) {
+	if useODirect {
+		warnODirectUnsupportedOnce("openDataRead-windows", os.ErrInvalid)
+	}
+
+	ptr, err := syscall.UTF16PtrFromString(name)
+	if err != nil {
+		return nil, &os.PathError{Op: "open", Path: name, Err: err}
+	}
+	h, err := syscall.CreateFile(
+		ptr,
+		syscall.GENERIC_READ,
+		syscall.FILE_SHARE_READ|syscall.FILE_SHARE_WRITE|syscall.FILE_SHARE_DELETE,
+		nil,
+		syscall.OPEN_EXISTING,
+		syscall.FILE_ATTRIBUTE_NORMAL,
+		0,
+	)
+	if err != nil {
+		return nil, &os.PathError{Op: "open", Path: name, Err: err}
+	}
+	return os.NewFile(uintptr(h), name), nil
+}
diff --git a/backend/posix/dir_unix.go b/backend/posix/dir_unix.go
index e8017434..ad5d0ceb 100644
--- a/backend/posix/dir_unix.go
+++ b/backend/posix/dir_unix.go
@@ -46,9 +46,7 @@ func isErrDirNotEmpty(err error) bool {
 	return errors.Is(err, syscall.ENOTEMPTY)
 }
 
-// openForRead opens a file for reading. On non-Windows systems, os.Open is
-// sufficient because POSIX allows removing (unlinking) a file that is still
-// open by another process.
-func openForRead(name string) (*os.File, error) {
-	return os.Open(name)
+// openForRead opens an object data file for reading.
+func openForRead(name string, useODirect bool) (*os.File, error) {
+	return openDataRead(name, useODirect)
 }
diff --git a/backend/posix/dir_windows.go b/backend/posix/dir_windows.go
index 3538620c..b394f161 100644
--- a/backend/posix/dir_windows.go
+++ b/backend/posix/dir_windows.go
@@ -110,22 +110,6 @@ func isErrNotDir(err error) bool {
 // is held open for streaming the GET response body. Without this flag,
 // Windows returns "The process cannot access the file because it is being
 // used by another process" on the Remove call.
-func openForRead(name string) (*os.File, error) {
-	ptr, err := syscall.UTF16PtrFromString(name)
-	if err != nil {
-		return nil, &os.PathError{Op: "open", Path: name, Err: err}
-	}
-	h, err := syscall.CreateFile(
-		ptr,
-		syscall.GENERIC_READ,
-		syscall.FILE_SHARE_READ|syscall.FILE_SHARE_WRITE|syscall.FILE_SHARE_DELETE,
-		nil,
-		syscall.OPEN_EXISTING,
-		syscall.FILE_ATTRIBUTE_NORMAL,
-		0,
-	)
-	if err != nil {
-		return nil, &os.PathError{Op: "open", Path: name, Err: err}
-	}
-	return os.NewFile(uintptr(h), name), nil
+func openForRead(name string, useODirect bool) (*os.File, error) {
+	return openDataRead(name, useODirect)
 }
diff --git a/backend/posix/odirect_linux_helpers.go b/backend/posix/odirect_linux_helpers.go
new file mode 100644
index 00000000..5160a51e
--- /dev/null
+++ b/backend/posix/odirect_linux_helpers.go
@@ -0,0 +1,29 @@
+// Copyright 2026 Versity Software
+// This file is licensed under the Apache License, Version 2.0
+// (the "License"); you may not use this file except in compliance
+// with the License.  You may obtain a copy of the License at
+//
+//   http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing,
+// software distributed under the License is distributed on an
+// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+// KIND, either express or implied.  See the License for the
+// specific language governing permissions and limitations
+// under the License.
+
+//go:build linux
+
+package posix
+
+import (
+	"errors"
+	"syscall"
+)
+
+// Shared by Linux O_DIRECT open paths in data reads and tmpfile creation.
+func isODirectUnsupportedOpenErr(err error) bool {
+	return errors.Is(err, syscall.EINVAL) ||
+		errors.Is(err, syscall.EOPNOTSUPP) ||
+		errors.Is(err, syscall.ENOTSUP)
+}
diff --git a/backend/posix/otmpfile_common.go b/backend/posix/otmpfile_common.go
index a76876dd..3f80243e 100644
--- a/backend/posix/otmpfile_common.go
+++ b/backend/posix/otmpfile_common.go
@@ -15,22 +15,83 @@
 package posix
 
 import (
+	"errors"
 	"fmt"
+	"io"
 	"math/rand"
 	"os"
+	"strconv"
+	"syscall"
 	"time"
 )
 
+const odirectMinWriteAlign = 512
+
 func (tmp *tmpfile) Write(b []byte) (int, error) {
 	if int64(len(b)) > tmp.size {
 		return 0, fmt.Errorf("write exceeds content length %v", tmp.size)
 	}
 
+	if tmp.useODirect && !isODirectLenAligned(len(b)) {
+		if err := tmp.switchToBufferedAtCurrentOffset(fmt.Sprintf("unaligned write length: len=%d len%%512=%d", len(b), len(b)%odirectMinWriteAlign)); err != nil {
+			return 0, err
+		}
+	}
+
 	n, err := tmp.f.Write(b)
+	if err != nil && n == 0 && tmp.useODirect && isODirectRuntimeFallbackErr(err) {
+		warnODirectUnsupportedOnce("tmpfile.Write", err)
+		if fallbackErr := tmp.switchToBufferedAtCurrentOffset("O_DIRECT write failure"); fallbackErr != nil {
+			return 0, fallbackErr
+		}
+
+		n, err = tmp.f.Write(b)
+	}
 	tmp.size -= int64(n)
 	return n, err
 }
 
+func (tmp *tmpfile) switchToBufferedAtCurrentOffset(reason string) error {
+	offset, seekErr := tmp.f.Seek(0, io.SeekCurrent)
+	if seekErr != nil {
+		return fmt.Errorf("capture write offset before fallback reopen: %w", seekErr)
+	}
+
+	name := tmp.f.Name()
+	f, openErr := os.OpenFile(name, os.O_RDWR, 0)
+	if openErr != nil {
+		return fmt.Errorf("reopen temp file in buffered mode after O_DIRECT fallback (%s): %w", reason, openErr)
+	}
+
+	if _, seekErr = f.Seek(offset, io.SeekStart); seekErr != nil {
+		f.Close()
+		return fmt.Errorf("restore write offset after fallback reopen: %w", seekErr)
+	}
+
+	if closeErr := tmp.f.Close(); closeErr != nil {
+		f.Close()
+		return fmt.Errorf("close O_DIRECT temp file after fallback reopen: %w", closeErr)
+	}
+
+	tmp.f = f
+	if tmp.isOTmp {
+		tmp.procFDName = strconv.Itoa(int(f.Fd()))
+	}
+	tmp.useODirect = false
+
+	return nil
+}
+
+func isODirectLenAligned(n int) bool {
+	return n%odirectMinWriteAlign == 0
+}
+
+func isODirectRuntimeFallbackErr(err error) bool {
+	return errors.Is(err, syscall.EINVAL) ||
+		errors.Is(err, syscall.EOPNOTSUPP) ||
+		errors.Is(err, syscall.ENOTSUP)
+}
+
 func (tmp *tmpfile) File() *os.File {
 	return tmp.f
 }
diff --git a/backend/posix/posix.go b/backend/posix/posix.go
index 8933de2d..bb34ca12 100644
--- a/backend/posix/posix.go
+++ b/backend/posix/posix.go
@@ -29,6 +29,7 @@ import (
 	"sort"
 	"strconv"
 	"strings"
+	"sync"
 	"syscall"
 	"time"
 
@@ -87,6 +88,10 @@ type Posix struct {
 	// support copy_file_range is mounted over NFSv4.2.
 	forceNoCopyFileRange bool
 
+	// enableODirect is a flag to open object data files with O_DIRECT.
+	// This is best-effort and falls back to buffered I/O when unsupported.
+	enableODirect bool
+
 	// enable posix level bucket name validations, not needed if the
 	// frontend handlers are already validating bucket names
 	validateBucketName bool
@@ -108,6 +113,10 @@ type Posix struct {
 	// rejected with an 'InvalidRequest' to comply with the S3 limit
 	// of 5 GiB.
 	copyObjectThreshold int64
+
+	// ioBufferSize is the buffer size used by buffered copy/read paths.
+	ioBufferSize int
+	ioBufferPool sync.Pool
 }
 
 var _ backend.Backend = &Posix{}
@@ -149,10 +158,17 @@ const (
 	doFalloc   = true
 	skipFalloc = false
 
+	odirectAllowed    odirectPolicy = true
+	odirectNotAllowed odirectPolicy = false
+
 	// defaultConcurrency is the default limit for concurrent POSIX actions.
 	defaultConcurrency = 5000
+	// defaultIOBufferSize is the default buffer size used by io.CopyBuffer paths.
+	defaultIOBufferSize = 1024 * 1024
 )
 
+type odirectPolicy bool
+
 // PosixOpts are the options for the Posix backend
 type PosixOpts struct {
 	// ChownUID sets the UID of the object to the UID of the user on PUT
@@ -172,6 +188,9 @@ type PosixOpts struct {
 	ForceNoTmpFile bool
 	// ForceNoCopyFileRange disables the use of io.Copy for multipart uploads parts
 	ForceNoCopyFileRange bool
+	// EnableODirect enables best-effort O_DIRECT for object data reads/writes.
+	// Disabled by default.
+	EnableODirect bool
 	// ValidateBucketNames enables minimal bucket name validation to prevent
 	// incorrect access to the filesystem. This is only needed if the
 	// frontend is not already validating bucket names.
@@ -194,9 +213,14 @@ type PosixOpts struct {
 	// attribute (e.g. files placed on the filesystem outside of versitygw).
 	// When empty, such objects are served with an empty ETag.
 	DefaultEtag string
+	// IOBufferSize sets the buffer size (in bytes) for copy/read paths that use
+	// io.CopyBuffer or buffered readers. Defaults to 1MiB when unset or invalid.
+	IOBufferSize int
 }
 
 func New(rootdir string, meta meta.MetadataStorer, opts PosixOpts) (*Posix, error) {
+	ioBufferSize := ioBufferSizeOrDefault(opts.IOBufferSize)
+
 	if opts.SideCarDir != "" && strings.HasPrefix(opts.SideCarDir, rootdir) {
 		return nil, fmt.Errorf("sidecar directory cannot be inside the gateway root directory")
 	}
@@ -255,10 +279,16 @@ func New(rootdir string, meta meta.MetadataStorer, opts PosixOpts) (*Posix, erro
 		newDirPerm:           opts.NewDirPerm,
 		forceNoTmpFile:       opts.ForceNoTmpFile,
 		forceNoCopyFileRange: opts.ForceNoCopyFileRange,
+		enableODirect:        opts.EnableODirect,
 		validateBucketName:   opts.ValidateBucketNames,
 		actionLimiter:        semaphore.NewWeighted(int64(concurrencyOrDefault(opts.Concurrency))),
 		copyObjectThreshold:  opts.CopyObjectThreshold,
 		defaultEtag:          opts.DefaultEtag,
+		ioBufferSize:         ioBufferSize,
+		ioBufferPool: sync.Pool{New: func() any {
+			b := make([]byte, ioBufferSize)
+			return &b
+		}},
 	}, nil
 }
 
@@ -270,6 +300,32 @@ func concurrencyOrDefault(n int) int {
 	return defaultConcurrency
 }
 
+func ioBufferSizeOrDefault(n int) int {
+	if n > 0 {
+		return n
+	}
+	return defaultIOBufferSize
+}
+
+func (p *Posix) getIOBuffer() []byte {
+	bp, ok := p.ioBufferPool.Get().(*[]byte)
+	if !ok || bp == nil || cap(*bp) < p.ioBufferSize {
+		return make([]byte, p.ioBufferSize)
+	}
+	return (*bp)[:p.ioBufferSize]
+}
+
+func (p *Posix) putIOBuffer(b []byte) {
+	if b == nil {
+		return
+	}
+	if cap(b) < p.ioBufferSize {
+		return
+	}
+	b = b[:p.ioBufferSize]
+	p.ioBufferPool.Put(&b)
+}
+
 func validateSubDir(root, dir string) (string, error) {
 	absDir, err := filepath.Abs(dir)
 	if err != nil {
@@ -945,12 +1001,13 @@ func (p *Posix) createObjVersion(bucket, key string, size int64, acc auth.Accoun
 	versioningKey := filepath.Join(genObjVersionKey(key), versionId)
 	versionTmpPath := filepath.Join(versionBucketPath, MetaTmpDir)
 	f, err := p.openTmpFile(versionTmpPath, versionBucketPath, versioningKey,
-		size, acc, doFalloc, p.forceNoTmpFile)
+		size, acc, doFalloc, p.forceNoTmpFile, odirectNotAllowed)
 	if err != nil {
 		return versionPath, err
 	}
 	defer f.cleanup()
 
+	// Prioritize copy_file_range for internal file-to-file version copies.
 	_, err = io.Copy(f.File(), sf)
 	if err != nil {
 		return versionPath, err
@@ -2092,7 +2149,7 @@ func (p *Posix) CompleteMultipartUploadWithCopy(ctx context.Context, input *s3.C
 	}
 
 	f, err := p.openTmpFile(filepath.Join(bucket, MetaTmpDir), bucket, object,
-		totalsize, acct, skipFalloc, p.forceNoTmpFile)
+		totalsize, acct, skipFalloc, p.forceNoTmpFile, odirectNotAllowed)
 	if err != nil {
 		if errors.Is(err, syscall.EDQUOT) {
 			return res, "", s3err.GetAPIError(s3err.ErrQuotaExceeded)
@@ -2119,12 +2176,13 @@ func (p *Posix) CompleteMultipartUploadWithCopy(ctx context.Context, input *s3.C
 				// Fail back to standard copy
 				debuglogger.Logf("custom data block move failed (%q/%q): %v, failing back to io.Copy()",
 					bucket, object, err)
-				fw := f.File()
-				fw.Seek(0, io.SeekEnd)
+				_, _ = f.File().Seek(0, io.SeekEnd)
 				if p.forceNoCopyFileRange {
-					_, err = io.Copy(fw, &onlyRead{pf})
+					_, err = io.Copy(f, &onlyRead{pf})
 				} else {
-					_, err = io.Copy(fw, pf)
+					// Keep both endpoints as *os.File here so
+					// io.Copy can use copy_file_range.
+					_, err = io.Copy(f.File(), pf)
 				}
 			}
 			if !idemp && err == nil {
@@ -2145,8 +2203,10 @@ func (p *Posix) CompleteMultipartUploadWithCopy(ctx context.Context, input *s3.C
 			}
 		} else {
 			if p.forceNoCopyFileRange {
-				_, err = io.Copy(f.File(), &onlyRead{pf})
+				_, err = io.Copy(f, &onlyRead{pf})
 			} else {
+				// Keep both endpoints as *os.File here so
+				// io.Copy can use copy_file_range.
 				_, err = io.Copy(f.File(), pf)
 			}
 		}
@@ -3030,7 +3090,7 @@ func (p *Posix) UploadPartWithPostFunc(ctx context.Context, input *s3.UploadPart
 	partPath := filepath.Join(mpPath, fmt.Sprintf("%v", *part))
 
 	f, err := p.openTmpFile(filepath.Join(bucket, objdir),
-		bucket, partPath, length, acct, doFalloc, p.forceNoTmpFile)
+		bucket, partPath, length, acct, doFalloc, p.forceNoTmpFile, odirectAllowed)
 	if err != nil {
 		if errors.Is(err, syscall.EDQUOT) {
 			drainBody(r)
@@ -3152,7 +3212,10 @@ func (p *Posix) UploadPartWithPostFunc(ctx context.Context, input *s3.UploadPart
 		}
 	}
 
-	_, err = io.Copy(f, tr)
+	buf := p.getIOBuffer()
+	defer p.putIOBuffer(buf)
+
+	_, err = io.CopyBuffer(f, tr, buf)
 	if err != nil {
 		if errors.Is(err, syscall.EDQUOT) {
 			drainBody(tr)
@@ -3415,7 +3478,7 @@ func (p *Posix) UploadPartCopy(ctx context.Context, upi *s3.UploadPartCopyInput)
 	}
 
 	f, err := p.openTmpFile(filepath.Join(*upi.Bucket, objdir),
-		*upi.Bucket, partPath, length, acct, doFalloc, p.forceNoTmpFile)
+		*upi.Bucket, partPath, length, acct, doFalloc, p.forceNoTmpFile, odirectNotAllowed)
 	if err != nil {
 		if errors.Is(err, syscall.EDQUOT) {
 			return s3response.CopyPartResult{}, s3err.GetAPIError(s3err.ErrQuotaExceeded)
@@ -3803,7 +3866,7 @@ func (p *Posix) PutObjectWithPostFunc(ctx context.Context, po s3response.PutObje
 	}
 
 	f, err := p.openTmpFile(filepath.Join(*po.Bucket, MetaTmpDir),
-		*po.Bucket, *po.Key, contentLength, acct, doFalloc, p.forceNoTmpFile)
+		*po.Bucket, *po.Key, contentLength, acct, doFalloc, p.forceNoTmpFile, odirectAllowed)
 	if err != nil {
 		if errors.Is(err, syscall.EDQUOT) {
 			drainBody(po.Body)
@@ -3832,7 +3895,10 @@ func (p *Posix) PutObjectWithPostFunc(ctx context.Context, po s3response.PutObje
 		rdr = hashRdr
 	}
 
-	_, err = io.Copy(f, rdr)
+	buf := p.getIOBuffer()
+	defer p.putIOBuffer(buf)
+
+	_, err = io.CopyBuffer(f, rdr, buf)
 	if err != nil {
 		if errors.Is(err, syscall.EDQUOT) {
 			drainBody(rdr)
@@ -4234,13 +4300,14 @@ func (p *Posix) DeleteObject(ctx context.Context, input *s3.DeleteObjectInput) (
 
 				f, err := p.openTmpFile(filepath.Join(bucket, MetaTmpDir),
 					bucket, object, srcObjVersion.Size(), acct, doFalloc,
-					p.forceNoTmpFile)
+					p.forceNoTmpFile, odirectNotAllowed)
 				if err != nil {
 					return nil, fmt.Errorf("open tmp file: %w", err)
 				}
 				defer f.cleanup()
 
-				_, err = io.Copy(f, sf)
+				// Prioritize copy_file_range for internal file-to-file version restores.
+				_, err = io.Copy(f.File(), sf)
 				if err != nil {
 					_ = sf.Close()
 					return nil, fmt.Errorf("copy object %w", err)
@@ -4678,7 +4745,7 @@ func (p *Posix) GetObject(ctx context.Context, input *s3.GetObjectInput) (*s3.Ge
 	// openForRead opens with FILE_SHARE_DELETE on Windows so that a concurrent
 	// DeleteObject can call os.Remove on this file while the GET response body
 	// is still being streamed. On POSIX, os.Open is sufficient.
-	f, err := openForRead(objPath)
+	f, err := openForRead(objPath, p.enableODirect)
 	if errors.Is(err, fs.ErrNotExist) {
 		return nil, s3err.GetAPIError(s3err.ErrNoSuchKey)
 	}
@@ -4781,11 +4848,11 @@ func (p *Posix) GetObject(ctx context.Context, input *s3.GetObjectInput) (*s3.Ge
 		}
 	}
 
-	// using an os.File allows zero-copy sendfile via io.Copy(os.File, net.Conn)
-	var body io.ReadCloser = f
-	if startOffset != 0 || length != objSize {
-		rdr := io.NewSectionReader(f, startOffset, length)
-		body = &backend.FileSectionReadCloser{R: rdr, F: f}
+	// Full-object responses can keep the underlying *os.File for sendfile.
+	// Linux range reads on O_DIRECT may need runtime fallback to buffered I/O.
+	body, err := buildGetObjectBody(f, objPath, startOffset, length, objSize, p.enableODirect, p.ioBufferSize)
+	if err != nil {
+		return nil, fmt.Errorf("build get object body: %w", err)
 	}
 
 	return &s3.GetObjectOutput{
diff --git a/backend/posix/posix_io_helpers.go b/backend/posix/posix_io_helpers.go
new file mode 100644
index 00000000..62eed318
--- /dev/null
+++ b/backend/posix/posix_io_helpers.go
@@ -0,0 +1,55 @@
+// Copyright 2026 Versity Software
+// This file is licensed under the Apache License, Version 2.0
+// (the "License"); you may not use this file except in compliance
+// with the License.  You may obtain a copy of the License at
+//
+//   http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing,
+// software distributed under the License is distributed on an
+// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+// KIND, either express or implied.  See the License for the
+// specific language governing permissions and limitations
+// under the License.
+
+package posix
+
+import (
+	"bufio"
+	"io"
+	"log"
+	"sync"
+)
+
+func withReadBufferSize(r io.ReadCloser, size int) io.ReadCloser {
+	if size <= 0 {
+		return r
+	}
+
+	return &bufferedReadCloser{
+		r: bufio.NewReaderSize(r, size),
+		c: r,
+	}
+}
+
+type bufferedReadCloser struct {
+	r *bufio.Reader
+	c io.Closer
+}
+
+func (b *bufferedReadCloser) Read(p []byte) (int, error) {
+	return b.r.Read(p)
+}
+
+func (b *bufferedReadCloser) Close() error {
+	return b.c.Close()
+}
+
+var odirectUnsupportedWarnByOp sync.Map
+
+func warnODirectUnsupportedOnce(op string, err error) {
+	v, _ := odirectUnsupportedWarnByOp.LoadOrStore(op, &sync.Once{})
+	v.(*sync.Once).Do(func() {
+		log.Printf("WARNING: O_DIRECT is enabled but unsupported (%s: %v); falling back to buffered I/O. This warning is shown once per operation.", op, err)
+	})
+}
diff --git a/backend/posix/with_otmpfile.go b/backend/posix/with_otmpfile.go
index 6554f023..497abeb1 100644
--- a/backend/posix/with_otmpfile.go
+++ b/backend/posix/with_otmpfile.go
@@ -42,6 +42,8 @@ type tmpfile struct {
 	bucket     string
 	objname    string
 	isOTmp     bool
+	procFDName string
+	useODirect bool
 	size       int64
 	doChown    bool
 	uid        int
@@ -54,11 +56,11 @@ var (
 	defaultFilePerm uint32 = 0644
 )
 
-func (p *Posix) openTmpFile(dir, bucket, obj string, size int64, acct auth.Account, dofalloc bool, forceNoTmpFile bool) (*tmpfile, error) {
+func (p *Posix) openTmpFile(dir, bucket, obj string, size int64, acct auth.Account, dofalloc bool, forceNoTmpFile bool, allowODirect odirectPolicy) (*tmpfile, error) {
 	uid, gid, doChown := p.getChownIDs(acct)
 
 	if forceNoTmpFile {
-		return p.openMkTemp(dir, bucket, obj, size, dofalloc, uid, gid, doChown)
+		return p.openMkTemp(dir, bucket, obj, size, dofalloc, uid, gid, doChown, allowODirect)
 	}
 
 	// O_TMPFILE allows for a file handle to an unnamed file in the filesystem.
@@ -67,14 +69,34 @@ func (p *Posix) openTmpFile(dir, bucket, obj string, size int64, acct auth.Accou
 	// file descriptor into the namespace.
 	// Not all filesystems support this, so fallback to CreateTemp for when
 	// this is not supported.
-	fd, err := unix.Open(dir, unix.O_RDWR|unix.O_TMPFILE|unix.O_CLOEXEC, defaultFilePerm)
+	openFlags := unix.O_RDWR | unix.O_TMPFILE | unix.O_CLOEXEC
+	useODirect := false
+	if p.enableODirect && bool(allowODirect) {
+		openFlags |= unix.O_DIRECT
+		useODirect = true
+	}
+
+	fd, err := unix.Open(dir, openFlags, defaultFilePerm)
 	if err != nil {
 		if errors.Is(err, syscall.EROFS) {
 			return nil, s3err.GetAPIError(s3err.ErrMethodNotAllowed)
 		}
 
-		// O_TMPFILE not supported, try fallback
-		return p.openMkTemp(dir, bucket, obj, size, dofalloc, uid, gid, doChown)
+		if p.enableODirect && bool(allowODirect) && isODirectUnsupportedOpenErr(err) {
+			warnODirectUnsupportedOnce("openTmpFile", err)
+
+			fd, err = unix.Open(dir, unix.O_RDWR|unix.O_TMPFILE|unix.O_CLOEXEC, defaultFilePerm)
+			if err == nil {
+				useODirect = false
+			} else if errors.Is(err, syscall.EROFS) {
+				return nil, s3err.GetAPIError(s3err.ErrMethodNotAllowed)
+			}
+		}
+
+		if err != nil {
+			// O_TMPFILE not supported, try fallback
+			return p.openMkTemp(dir, bucket, obj, size, dofalloc, uid, gid, doChown, allowODirect)
+		}
 	}
 
 	// for O_TMPFILE, filename is /proc/self/fd/<fd> to be used
@@ -86,6 +108,8 @@ func (p *Posix) openTmpFile(dir, bucket, obj string, size int64, acct auth.Accou
 		bucket:     bucket,
 		objname:    obj,
 		isOTmp:     true,
+		procFDName: strconv.Itoa(fd),
+		useODirect: useODirect,
 		size:       size,
 		doChown:    doChown,
 		uid:        uid,
@@ -109,7 +133,7 @@ func (p *Posix) openTmpFile(dir, bucket, obj string, size int64, acct auth.Accou
 	return tmp, nil
 }
 
-func (p *Posix) openMkTemp(dir, bucket, obj string, size int64, dofalloc bool, uid, gid int, doChown bool) (*tmpfile, error) {
+func (p *Posix) openMkTemp(dir, bucket, obj string, size int64, dofalloc bool, uid, gid int, doChown bool, allowODirect odirectPolicy) (*tmpfile, error) {
 	err := backend.MkdirAll(dir, uid, gid, doChown, p.newDirPerm)
 	if err != nil {
 		if errors.Is(err, syscall.EROFS) {
@@ -125,14 +149,41 @@ func (p *Posix) openMkTemp(dir, bucket, obj string, size int64, dofalloc bool, u
 		}
 		return nil, err
 	}
+
+	useODirect := false
+	if p.enableODirect && bool(allowODirect) {
+		name := f.Name()
+		if err := f.Close(); err != nil {
+			os.Remove(name)
+			return nil, fmt.Errorf("close temp file before O_DIRECT reopen: %w", err)
+		}
+
+		fd, err := unix.Open(name, unix.O_RDWR|unix.O_CLOEXEC|unix.O_DIRECT, defaultFilePerm)
+		if err == nil {
+			f = os.NewFile(uintptr(fd), name)
+			useODirect = true
+		} else if isODirectUnsupportedOpenErr(err) {
+			warnODirectUnsupportedOnce("openMkTemp", err)
+			f, err = os.OpenFile(name, os.O_RDWR, 0)
+			if err != nil {
+				os.Remove(name)
+				return nil, fmt.Errorf("reopen temp file after O_DIRECT fallback: %w", err)
+			}
+		} else {
+			os.Remove(name)
+			return nil, fmt.Errorf("open temp file with O_DIRECT: %w", err)
+		}
+	}
+
 	tmp := &tmpfile{
-		f:       f,
-		bucket:  bucket,
-		objname: obj,
-		size:    size,
-		doChown: doChown,
-		uid:     uid,
-		gid:     gid,
+		f:          f,
+		bucket:     bucket,
+		objname:    obj,
+		useODirect: useODirect,
+		size:       size,
+		doChown:    doChown,
+		uid:        uid,
+		gid:        gid,
 	}
 	// falloc is best effort, its fine if this fails
 	if size > 0 && dofalloc {
@@ -237,8 +288,12 @@ func (tmp *tmpfile) link() error {
 		if err != nil {
 			return fmt.Errorf("open parent dir: %w", err)
 		}
+		srcFDName := tmp.procFDName
+		if srcFDName == "" {
+			srcFDName = filepath.Base(tmp.f.Name())
+		}
 		err = linkatOTmpfile(int(procdir.Fd()), int(dirf.Fd()),
-			filepath.Base(tmp.f.Name()), filepath.Base(objPath))
+			srcFDName, filepath.Base(objPath))
 		dirf.Close()
 		if errors.Is(err, syscall.ENOENT) {
 			// The directory was removed between open and linkat; backoff and retry.
@@ -254,7 +309,7 @@ func (tmp *tmpfile) link() error {
 		}
 		if err != nil {
 			return fmt.Errorf("link tmpfile (fd %q as %q): %w",
-				filepath.Base(tmp.f.Name()), objPath, err)
+				srcFDName, objPath, err)
 		}
 		break
 	}
diff --git a/backend/posix/without_otmpfile.go b/backend/posix/without_otmpfile.go
index bc7cf579..05748b22 100644
--- a/backend/posix/without_otmpfile.go
+++ b/backend/posix/without_otmpfile.go
@@ -36,9 +36,13 @@ const (
 )
 
 type tmpfile struct {
-	f          *os.File
-	bucket     string
-	objname    string
+	f       *os.File
+	bucket  string
+	objname string
+	// Retained for compatibility with shared tmpfile methods in otmpfile_common.
+	isOTmp     bool
+	procFDName string
+	useODirect bool
 	size       int64
 	newDirPerm fs.FileMode
 	uid        int
@@ -46,9 +50,13 @@ type tmpfile struct {
 	doChown    bool
 }
 
-func (p *Posix) openTmpFile(dir, bucket, obj string, size int64, acct auth.Account, _ bool, _ bool) (*tmpfile, error) {
+func (p *Posix) openTmpFile(dir, bucket, obj string, size int64, acct auth.Account, _ bool, _ bool, allowODirect odirectPolicy) (*tmpfile, error) {
 	uid, gid, doChown := p.getChownIDs(acct)
 
+	if p.enableODirect && bool(allowODirect) {
+		warnODirectUnsupportedOnce("openTmpFile-nonlinux", os.ErrInvalid)
+	}
+
 	// Create a temp file for upload while in progress (see link comments below).
 	var err error
 	err = backend.MkdirAll(dir, uid, gid, doChown, p.newDirPerm)
@@ -80,6 +88,9 @@ func (p *Posix) openTmpFile(dir, bucket, obj string, size int64, acct auth.Accou
 		f:          f,
 		bucket:     bucket,
 		objname:    obj,
+		isOTmp:     false,
+		procFDName: "",
+		useODirect: false,
 		size:       size,
 		newDirPerm: p.newDirPerm,
 		uid:        uid,
diff --git a/cmd/versitygw/posix.go b/cmd/versitygw/posix.go
index c1541edd..a28227ea 100644
--- a/cmd/versitygw/posix.go
+++ b/cmd/versitygw/posix.go
@@ -33,7 +33,9 @@ var (
 	nometa               bool
 	forceNoTmpFile       bool
 	forceNoCopyFileRange bool
+	enableODirect        bool
 	actionsConcurrency   int
+	ioBufferSize         int
 	defaultEtag          string
 )
 
@@ -98,6 +100,13 @@ will be translated into the file /mnt/fs/gwroot/mybucket/a/b/c/myobject`,
 				Value:       5000,
 				Destination: &actionsConcurrency,
 			},
+			&cli.IntFlag{
+				Name:        "io-buffer-size",
+				Usage:       "buffer size in bytes used by POSIX put/get/part read and write paths (<=0 uses backend default 1MiB)",
+				EnvVars:     []string{"VGW_POSIX_IO_BUFFER_SIZE"},
+				Value:       1024 * 1024,
+				Destination: &ioBufferSize,
+			},
 			&cli.BoolFlag{
 				Name:        "nometa",
 				Usage:       "disable metadata storage",
@@ -116,6 +125,12 @@ will be translated into the file /mnt/fs/gwroot/mybucket/a/b/c/myobject`,
 				EnvVars:     []string{"VGW_DISABLE_COPY_FILE_RANGE"},
 				Destination: &forceNoCopyFileRange,
 			},
+			&cli.BoolFlag{
+				Name:        "enable-odirect",
+				Usage:       "enable best-effort O_DIRECT for object data reads/writes",
+				EnvVars:     []string{"VGW_ENABLE_O_DIRECT"},
+				Destination: &enableODirect,
+			},
 			&cli.StringFlag{
 				Name:        "default-etag",
 				Usage:       "default ETag value returned for objects that do not have a stored etag attribute (e.g. files placed on the filesystem outside of versitygw)",
@@ -153,8 +168,10 @@ func runPosix(ctx *cli.Context) error {
 		NewDirPerm:           fs.FileMode(dirPerms),
 		ForceNoTmpFile:       forceNoTmpFile,
 		ForceNoCopyFileRange: forceNoCopyFileRange,
+		EnableODirect:        enableODirect,
 		ValidateBucketNames:  disableStrictBucketNames,
 		Concurrency:          actionsConcurrency,
+		IOBufferSize:         ioBufferSize,
 		CopyObjectThreshold:  copyObjectThreshold,
 		DefaultEtag:          defaultEtag,
 	}
diff --git a/extra/example.conf b/extra/example.conf
index d5d2d866..4cebfc94 100644
--- a/extra/example.conf
+++ b/extra/example.conf
@@ -602,6 +602,12 @@ ROOT_SECRET_ACCESS_KEY=
 # memory use.
 #VGW_POSIX_CONCURRENCY=5000
 
+# The VGW_POSIX_IO_BUFFER_SIZE option sets the data transfer buffer size used
+# by the posix backend for PutObject, UploadPart, and GetObject read/write
+# paths. The default is 1048576 bytes (1 MiB). When set to 0 or a negative
+# value, the backend falls back to the same default.
+#VGW_POSIX_IO_BUFFER_SIZE=1048576
+
 # The gateway will use O_TMPFILE for writing objects while uploading and
 # link the file to the final object name when the upload is complete if the
 # filesystem supports O_TMPFILE. This creates an atomic object creation
@@ -623,6 +629,15 @@ ROOT_SECRET_ACCESS_KEY=
 # NFS servers that may hang on this call.
 #VGW_DISABLE_COPY_FILE_RANGE=false
 
+# The VGW_ENABLE_O_DIRECT option enables best-effort O_DIRECT for object data
+# reads and writes. This is disabled by default. When enabled, versitygw
+# attempts to open object data files with O_DIRECT and automatically falls back
+# to buffered I/O when O_DIRECT is not supported by the filesystem/open call.
+# Some systems may still enforce alignment constraints for direct I/O. The
+# VGW_POSIX_IO_BUFFER_SIZE setting can be used to tune buffered read/write
+# chunk sizing while keeping O_DIRECT best-effort behavior enabled.
+#VGW_ENABLE_O_DIRECT=false
+
 # The VGW_DEFAULT_ETAG option sets the ETag value returned for objects that do
 # not have a stored etag attribute. This applies to files that were placed on
 # the filesystem outside of versitygw and therefore lack S3 metadata. Some S3