diff --git a/cmd/rigtest/rigtest.go b/cmd/rigtest/rigtest.go
index a9f72265..7c29be78 100644
--- a/cmd/rigtest/rigtest.go
+++ b/cmd/rigtest/rigtest.go
@@ -1,7 +1,6 @@
 package main
 
 import (
-	"bytes"
 	"crypto/rand"
 	"crypto/sha256"
 	"errors"
@@ -286,64 +285,71 @@ func main() {
 		require.NoError(t, h.Configurer.DeleteFile(h, fn))
 		require.False(t, h.Configurer.FileExist(h, fn))
 
-		testFileSize := int64(1 << (10 * 2)) // 1MB
 		fsyses := []rigfs.Fsys{h.Fsys(), h.SudoFsys()}
 
 		for idx, fsys := range fsyses {
-			t.Run("fsys functions (%d) on %s", idx+1, h)
+			for _, testFileSize := range []int64{
+				int64(500),           // less than one block on most filesystems
+				int64(1 << (10 * 2)), // exactly 1MB
+				int64(4096),          // exactly one block on most filesystems
+				int64(4097),          // plus 1
+			} {
+				t.Run("fsys (%d) functions for file size %d on %s", idx+1, testFileSize, h)
 
-			origin := io.LimitReader(rand.Reader, testFileSize)
-			shasum := sha256.New()
-			reader := io.TeeReader(origin, shasum)
+				origin := io.LimitReader(rand.Reader, testFileSize)
+				shasum := sha256.New()
+				reader := io.TeeReader(origin, shasum)
 
-			destf, err := fsys.OpenFile(fn, rigfs.ModeCreate, 0644)
-			require.NoError(t, err, "open file")
+				destf, err := fsys.OpenFile(fn, rigfs.ModeCreate, 0644)
+				require.NoError(t, err, "open file")
 
-			n, err := io.Copy(destf, reader)
-			require.NoError(t, err, "io.copy file from local to remote")
-			require.Equal(t, testFileSize, n, "file size not as expected after copy")
+				n, err := io.Copy(destf, reader)
+				require.NoError(t, err, "io.copy file from local to remote")
+				require.Equal(t, testFileSize, n, "file size not as expected after copy")
 
-			require.NoError(t, destf.Close(), "error while closing file")
+				require.NoError(t, destf.Close(), "error while closing file")
 
-			fstat, err := fsys.Stat(fn)
-			require.NoError(t, err, "stat error")
-			require.Equal(t, testFileSize, fstat.Size(), "file size not as expected in stat result")
+				fstat, err := fsys.Stat(fn)
+				require.NoError(t, err, "stat error")
+				require.Equal(t, testFileSize, fstat.Size(), "file size not as expected in stat result")
 
-			destSum, err := fsys.Sha256(fn)
-			require.NoError(t, err, "sha256 error")
+				destSum, err := fsys.Sha256(fn)
+				require.NoError(t, err, "sha256 error")
 
-			require.Equal(t, fmt.Sprintf("%x", shasum.Sum(nil)), destSum, "sha256 mismatch after io.copy from local to remote")
+				require.Equal(t, fmt.Sprintf("%x", shasum.Sum(nil)), destSum, "sha256 mismatch after io.copy from local to remote")
 
-			destf, err = fsys.OpenFile(fn, rigfs.ModeRead, 0644)
-			require.NoError(t, err, "open file for read")
+				destf, err = fsys.OpenFile(fn, rigfs.ModeRead, 0644)
+				require.NoError(t, err, "open file for read")
 
-			readSha := sha256.New()
-			n, err = io.Copy(readSha, destf)
-			require.NoError(t, err, "io.copy file from remote to local")
+				readSha := sha256.New()
+				n, err = io.Copy(readSha, destf)
+				require.NoError(t, err, "io.copy file from remote to local")
 
-			require.Equal(t, testFileSize, n, "file size not as expected after copy from remote to local")
+				require.Equal(t, testFileSize, n, "file size not as expected after copy from remote to local")
 
-			fstat, err = destf.Stat()
-			require.NoError(t, err, "stat error after read")
-			require.Equal(t, testFileSize, fstat.Size(), "file size not as expected in stat result after read")
-			require.True(t, bytes.Equal(readSha.Sum(nil), shasum.Sum(nil)), "sha256 mismatch after io.copy from remote to local")
+				fstat, err = destf.Stat()
+				require.NoError(t, err, "stat error after read")
+				require.Equal(t, testFileSize, fstat.Size(), "file size not as expected in stat result after read")
+				require.Equal(t, readSha.Sum(nil), shasum.Sum(nil), "sha256 mismatch after io.copy from remote to local")
 
-			_, err = destf.Seek(0, 0)
-			require.NoError(t, err, "seek")
+				_, err = destf.Seek(0, 0)
+				require.NoError(t, err, "seek")
 
-			readSha.Reset()
+				readSha.Reset()
 
-			n, err = io.Copy(readSha, destf)
-			require.NoError(t, err, "io.copy file from remote to local after seek")
+				n, err = io.Copy(readSha, destf)
+				require.NoError(t, err, "io.copy file from remote to local after seek")
 
-			require.Equal(t, testFileSize, n, "file size not as expected after copy from remote to local after seek")
+				require.Equal(t, testFileSize, n, "file size not as expected after copy from remote to local after seek")
 
-			require.True(t, bytes.Equal(readSha.Sum(nil), shasum.Sum(nil)), "sha256 mismatch after io.copy from remote to local after seek")
+				require.Equal(t, readSha.Sum(nil), shasum.Sum(nil), "sha256 mismatch after io.copy from remote to local after seek")
 
-			require.NoError(t, destf.Close(), "close after seek + read")
-			require.NoError(t, fsys.Remove(fn), "remove file")
-			_, err = destf.Stat()
-			require.ErrorIs(t, err, fs.ErrNotExist, "file still exists")
+				require.NoError(t, destf.Close(), "close after seek + read")
+				require.NoError(t, fsys.Remove(fn), "remove file")
+				_, err = destf.Stat()
+				require.ErrorIs(t, err, fs.ErrNotExist, "file still exists")
+			}
+			t.Run("fsys (%d) dir ops on %s", idx+1, h)
 
 			// fsys dirops
 			require.NoError(t, fsys.MkDirAll("tmpdir/nested", 0644), "make nested dir")
diff --git a/pkg/rigfs/posixfsys.go b/pkg/rigfs/posixfsys.go
index ddba60dd..37c1f78d 100644
--- a/pkg/rigfs/posixfsys.go
+++ b/pkg/rigfs/posixfsys.go
@@ -8,6 +8,8 @@ import (
 	"io"
 	"io/fs"
 	"os"
+	"path/filepath"
+	"strconv"
 	"strings"
 	"time"
 
@@ -38,6 +40,8 @@ func NewPosixFsys(conn connection, opts ...exec.Option) *PosixFsys {
 	return &PosixFsys{conn: conn, opts: opts}
 }
 
+const defaultBlockSize = 4096
+
 // PosixFile implements fs.File for a remote file
 type PosixFile struct {
 	fsys   *PosixFsys
@@ -47,6 +51,8 @@ type PosixFile struct {
 	pos    int64
 	size   int64
 	mode   FileMode
+
+	blockSize int
 }
 
 // PosixDir implements fs.ReadDirFile for a remote directory
@@ -83,6 +89,22 @@ func (f *PosixDir) ReadDir(n int) ([]fs.DirEntry, error) {
 	return f.entries[old:f.hw], nil
 }
 
+func (f *PosixFile) fsBlockSize() int {
+	if f.blockSize > 0 {
+		return f.blockSize
+	}
+
+	out, err := f.fsys.conn.ExecOutput(fmt.Sprintf(`stat -c "%%s" %[1]s 2> /dev/null || stat -f "%%k" %[1]s`, shellescape.Quote(filepath.Dir(f.path))), f.fsys.opts...)
+	if err != nil {
+		// fall back to default
+		f.blockSize = defaultBlockSize
+	} else if bs, err := strconv.Atoi(strings.TrimSpace(out)); err == nil {
+		f.blockSize = bs
+	}
+
+	return f.blockSize
+}
+
 func (f *PosixFile) isReadable() bool {
 	return f.mode&ModeRead != 0
 }
@@ -91,13 +113,18 @@ func (f *PosixFile) isWritable() bool {
 	return f.mode&ModeWrite != 0
 }
 
-const blockSize = 4096
-
 func (f *PosixFile) ddParams(offset int64, numBytes int) (int, int64, int) {
-	skip := offset / int64(blockSize)
-	count := (numBytes + blockSize - 1) / blockSize
+	bs := f.fsBlockSize()
 
-	return blockSize, skip, count
+	if numBytes < bs {
+		bs = numBytes
+		skip := offset / int64(bs)
+		return bs, skip, 1
+	}
+
+	skip := offset / int64(bs)
+	count := numBytes / bs
+	return bs, skip, count
 }
 
 // Stat returns a FileInfo describing the named file
@@ -113,9 +140,13 @@ func (f *PosixFile) Read(p []byte) (int, error) {
 	if !f.isReadable() {
 		return 0, fmt.Errorf("%w: file %s is not open for reading", ErrCommandFailed, f.path)
 	}
-	bs, skip, count := f.ddParams(f.pos, len(p))
 	errbuf := bytes.NewBuffer(nil)
+
+	bs, skip, count := f.ddParams(f.pos, len(p))
+	toRead := bs * count
 	buf := bytes.NewBuffer(nil)
+	errbuf.Reset()
+
 	cmd, err := f.fsys.conn.ExecStreams(fmt.Sprintf("dd if=%s bs=%d skip=%d count=%d", shellescape.Quote(f.path), bs, skip, count), nil, buf, errbuf, f.fsys.opts...)
 	if err != nil {
 		return 0, fmt.Errorf("%w: failed to execute dd: %w (%s)", ErrCommandFailed, err, errbuf.String())
@@ -123,32 +154,39 @@ func (f *PosixFile) Read(p []byte) (int, error) {
 	if err := cmd.Wait(); err != nil {
 		return 0, fmt.Errorf("%w: read (dd): %w (%s)", ErrCommandFailed, err, errbuf.String())
 	}
-	f.pos += int64(buf.Len())
-	if buf.Len() < len(p) {
+
+	readBytes := copy(p, buf.Bytes())
+	f.pos += int64(readBytes)
+	if readBytes < len(p) || readBytes < toRead {
 		f.isEOF = true
+		return readBytes, io.EOF
 	}
-	return copy(p, buf.Bytes()), nil
+	return readBytes, nil
 }
 
 func (f *PosixFile) Write(p []byte) (int, error) {
 	if !f.isWritable() {
 		return 0, fmt.Errorf("%w: file %s is not open for writing", ErrCommandFailed, f.path)
 	}
+
 	bs, skip, count := f.ddParams(f.pos, len(p))
+	toWrite := bs * count
+
 	errbuf := bytes.NewBuffer(nil)
-	cmd, err := f.fsys.conn.ExecStreams(fmt.Sprintf("dd if=/dev/stdin of=%s bs=%d count=%d seek=%d conv=notrunc", f.path, bs, count, skip), io.NopCloser(bytes.NewReader(p)), io.Discard, errbuf, f.fsys.opts...)
+	limitedReader := bytes.NewReader(p[:toWrite])
+	cmd, err := f.fsys.conn.ExecStreams(fmt.Sprintf("dd if=/dev/stdin of=%s bs=%d count=%d seek=%d conv=notrunc", f.path, bs, count, skip), io.NopCloser(limitedReader), io.Discard, errbuf, f.fsys.opts...)
 	if err != nil {
 		return 0, fmt.Errorf("%w: write (dd): %w", ErrCommandFailed, err)
 	}
 	if err := cmd.Wait(); err != nil {
 		return 0, fmt.Errorf("%w: write (dd): %w (%s)", ErrCommandFailed, err, errbuf.String())
 	}
-	written := len(p)
-	f.pos += int64(written)
+	f.pos += int64(toWrite)
+
 	if f.pos > f.size {
 		f.size = f.pos
 	}
-	return written, nil
+	return toWrite, nil
 }
 
 // CopyFromN copies n bytes from the remote file. The alt writer can be used for progress
diff --git a/test/test.sh b/test/test.sh
index ff9af77a..61c15a2a 100755
--- a/test/test.sh
+++ b/test/test.sh
@@ -30,6 +30,16 @@ sanity_check() {
   RET=$exit_code
 }
 
+rig_test_key_from_path() {
+  color_echo "- Testing regular keypath and host functions"
+  make create-host
+  mv .ssh/identity .ssh/identity2
+  set +e
+  ./rigtest -host 127.0.0.1:$(ssh_port node0) -user root -keypath .ssh/identity2 
+  local exit_code=$?
+  set -e
+  RET=$exit_code
+}
 
 rig_test_agent_with_public_key() {
   color_echo "- Testing connection using agent and providing a path to public key"
@@ -159,18 +169,6 @@ rig_test_ssh_config_no_strict() {
   RET=$exit_code
 }
 
-
-rig_test_key_from_path() {
-  color_echo "- Testing regular keypath and host functions"
-  make create-host
-  mv .ssh/identity .ssh/identity2
-  set +e
-  ./rigtest -host 127.0.0.1:$(ssh_port node0) -user root -keypath .ssh/identity2 
-  local exit_code=$?
-  set -e
-  RET=$exit_code
-}
-
 rig_test_key_from_memory() {
   color_echo "- Testing connecting using a key from string"
   make create-host
@@ -187,7 +185,7 @@ rig_test_key_from_default_location() {
   make create-host
   mv .ssh/identity .ssh/id_ecdsa
   set +e
-  HOME=$(pwd) ./rigtest -host 127.0.0.1:$(ssh_port node0) -user root
+  HOME=$(pwd) ./rigtest -host 127.0.0.1:$(ssh_port node0) -user root -connect
   local exit_code=$?
   set -e
   RET=$exit_code