diff --git a/tests/runfiles/common.run b/tests/runfiles/common.run
index b8310264a89f..c625f33063c9 100644
--- a/tests/runfiles/common.run
+++ b/tests/runfiles/common.run
@@ -40,6 +40,10 @@ tests = ['alloc_class_001_pos', 'alloc_class_002_neg', 'alloc_class_003_pos',
     'alloc_class_013_pos']
 tags = ['functional', 'alloc_class']
 
+[tests/functional/append]
+tests = ['file_append', 'threadsappend_001_pos']
+tags = ['functional', 'append']
+
 [tests/functional/arc]
 tests = ['dbufstats_001_pos', 'dbufstats_002_pos', 'dbufstats_003_pos',
     'arcstats_runtime_tuning']
@@ -884,10 +888,6 @@ tests = ['suid_write_to_suid', 'suid_write_to_sgid', 'suid_write_to_suid_sgid',
     'suid_write_to_none', 'suid_write_zil_replay']
 tags = ['functional', 'suid']
 
-[tests/functional/threadsappend]
-tests = ['threadsappend_001_pos']
-tags = ['functional', 'threadsappend']
-
 [tests/functional/trim]
 tests = ['autotrim_integrity', 'autotrim_config', 'autotrim_trim_integrity',
     'trim_integrity', 'trim_config', 'trim_l2arc']
diff --git a/tests/runfiles/sanity.run b/tests/runfiles/sanity.run
index 0ed693c2f4ae..f5dcfa5be4b7 100644
--- a/tests/runfiles/sanity.run
+++ b/tests/runfiles/sanity.run
@@ -584,7 +584,7 @@ tests = ['suid_write_to_suid', 'suid_write_to_sgid', 'suid_write_to_suid_sgid',
     'suid_write_to_none']
 tags = ['functional', 'suid']
 
-[tests/functional/threadsappend]
+[tests/functional/append]
 tests = ['threadsappend_001_pos']
 tags = ['functional', 'threadsappend']
 
diff --git a/tests/test-runner/bin/zts-report.py.in b/tests/test-runner/bin/zts-report.py.in
index b0941a4d5f4b..0229d18e2829 100755
--- a/tests/test-runner/bin/zts-report.py.in
+++ b/tests/test-runner/bin/zts-report.py.in
@@ -235,7 +235,7 @@ maybe = {
     'snapshot/snapshot_010_pos': ['FAIL', 7961],
     'snapused/snapused_004_pos': ['FAIL', 5513],
     'tmpfile/setup': ['SKIP', tmpfile_reason],
-    'threadsappend/threadsappend_001_pos': ['FAIL', 6136],
+    'append/threadsappend_001_pos': ['FAIL', 6136],
     'trim/setup': ['SKIP', trim_reason],
     'upgrade/upgrade_projectquota_001_pos': ['SKIP', project_id_reason],
     'user_namespace/setup': ['SKIP', user_ns_reason],
diff --git a/tests/zfs-tests/cmd/.gitignore b/tests/zfs-tests/cmd/.gitignore
index e28fed8f12d8..c2ef0e8c8349 100644
--- a/tests/zfs-tests/cmd/.gitignore
+++ b/tests/zfs-tests/cmd/.gitignore
@@ -4,6 +4,7 @@
 /devname2devid
 /dir_rd_update
 /draid
+/file_append
 /file_check
 /file_trunc
 /file_write
diff --git a/tests/zfs-tests/cmd/file/file_append.c b/tests/zfs-tests/cmd/file/file_append.c
new file mode 100644
index 000000000000..32433e4fa2f6
--- /dev/null
+++ b/tests/zfs-tests/cmd/file/file_append.c
@@ -0,0 +1,206 @@
+/*
+ * CDDL HEADER START
+ *
+ * The contents of this file are subject to the terms of the
+ * Common Development and Distribution License (the "License").
+ * You may not use this file except in compliance with the License.
+ *
+ * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
+ * or http://www.opensolaris.org/os/licensing.
+ * See the License for the specific language governing permissions
+ * and limitations under the License.
+ *
+ * When distributing Covered Code, include this CDDL HEADER in each
+ * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
+ * If applicable, add the following below this CDDL HEADER, with the
+ * fields enclosed by brackets "[]" replaced with your own identifying
+ * information: Portions Copyright [yyyy] [name of copyright owner]
+ *
+ * CDDL HEADER END
+ */
+
+/*
+ * Copyright (c) 2022 by Triad National Security, LLC
+ */
+
+#include "file_common.h"
+#include <unistd.h>
+#include <sys/sysmacros.h>
+
+static char *filename = NULL;
+static int expected_offset = -1;
+static int blocksize = 131072; /* 128KiB */
+static int numblocks = 8;
+static const char *execname = "file_append";
+static int use_odirect = 0;
+
+static void
+usage(void)
+{
+	(void) fprintf(stderr,
+	    "usage %s -f filename -e expected_offset [-b blocksize] \n"
+	    "         [-n numblocks] [-d use_odirect] [-h help]\n"
+	    "\n"
+	    "Opens a file using O_APPEND and writes numblocks blocksize\n"
+	    "blocks to filename.\n"
+	    "Checks if expected_offst == lseek(fd, 0, SEEK_CUR)).\n"
+	    "\n"
+	    "    filename:         File to open with O_APPEND and write to.\n"
+	    "    expected_offset:  Expected file offset after writing\n"
+	    "                      blocksize numblocks to filename\n"
+	    "    blocksize:        Size of each block to writei (must be at\n"
+	    "                      least >= 512). If using use_odirect (-d)\n"
+	    "                      must be a mutltiple of _SC_PAGE_SIZE\n"
+	    "    numblocks:        Total number of blocksized blocks to\n"
+	    "                      write.\n"
+	    "    use_odirect:      Open file using O_DIRECT.\n"
+	    "    help:             Print usage information and exit.\n"
+	    "\n"
+	    "    Required parameters:\n"
+	    "    filename\n"
+	    "    expected_offset\n"
+	    "\n"
+	    "    Default values:\n"
+	    "    blocksize   -> 131072 (128 KiB)\n"
+	    "    numblocks   -> 8\n"
+	    "    use_odirect -> False\n",
+	    execname);
+	(void) exit(1);
+}
+
+static void
+parse_options(int argc, char *argv[])
+{
+	int c;
+	int errflag = 0;
+	extern char *optarg;
+	extern int optind, optopt;
+
+	while ((c = getopt(argc, argv, "b:de:f:hn:")) != -1) {
+		switch (c) {
+			case 'b':
+				blocksize = atoi(optarg);
+				break;
+			case 'd':
+				use_odirect = 1;
+				break;
+			case 'e':
+				expected_offset = atoi(optarg);
+				break;
+			case 'f':
+				filename = optarg;
+				break;
+			case 'h':
+				(void) usage();
+				break;
+			case 'n':
+				numblocks = atoi(optarg);
+				break;
+			case ':':
+				(void) fprintf(stderr,
+				    "Option -%c requires an operand\n",
+				    optopt);
+				errflag++;
+				break;
+			case '?':
+			default:
+				(void) fprintf(stderr,
+				    "Unrecognized option: -%c\n", optopt);
+				errflag++;
+				break;
+		}
+	}
+
+	if (errflag)
+		(void) usage();
+
+	if (use_odirect && ((blocksize % sysconf(_SC_PAGE_SIZE)) != 0)) {
+		(void) fprintf(stderr,
+		    "blocksize parameter invalid when using O_DIRECT.\n");
+		(void) usage();
+	}
+
+	if (blocksize < 512 || expected_offset < 0 || filename == NULL ||
+	    numblocks <= 0) {
+		(void) fprintf(stderr,
+		    "Required parameters(s) missing or invalid value for "
+		    "parameter.\n");
+		(void) usage();
+	}
+}
+
+int
+main(int argc, char *argv[])
+{
+	int		err;
+	const char	*datapattern = "0xf00ba3";
+	int		fd = -1;
+	int		fd_flags = O_WRONLY | O_CREAT | O_APPEND;
+	int		buf_offset = 0;
+	char		*buf;
+
+	parse_options(argc, argv);
+
+	if (use_odirect)
+		fd_flags |= O_DIRECT;
+
+	fd = open(filename, fd_flags, 0666);
+	if (fd == -1) {
+		(void) fprintf(stderr, "%s: %s: ", execname, filename);
+		perror("open");
+		(void) exit(2);
+	}
+
+	err = posix_memalign((void **)&buf, sysconf(_SC_PAGE_SIZE),
+	    blocksize);
+
+	if (err != 0) {
+		(void) fprintf(stderr,
+		    "%s: %s\n", execname, strerror(err));
+		(void) exit(2);
+	}
+
+	/* Putting known data pattern in buffer */
+	int left = blocksize;
+	while (left) {
+		size_t amt = MIN(strlen(datapattern), left);
+		memcpy(&buf[buf_offset], datapattern, amt);
+		buf_offset += amt;
+		left -= amt;
+	}
+
+	for (int i = 0; i < numblocks; i++) {
+		int wrote = write(fd, buf, blocksize);
+
+		if (wrote != blocksize) {
+			if (wrote < 0) {
+				perror("write");
+			} else {
+				(void) fprintf(stderr,
+				    "%s: unexpected short write, wrote %d "
+				    "byte, expected %d\n", execname, wrote,
+				    blocksize);
+			}
+			(void) exit(2);
+		}
+	}
+
+	/* Getting current file offset */
+	off_t off = lseek(fd, 0, SEEK_CUR);
+
+	if (off == -1) {
+		perror("output seek");
+		(void) exit(2);
+	} else if (off != expected_offset) {
+		(void) fprintf(stderr,
+		    "%s: expected offset %d but current offset in %s is set "
+		    "to %ld\n", execname, expected_offset, filename,
+		    (long int)off);
+		(void) exit(2);
+	}
+
+	(void) close(fd);
+	free(buf);
+
+	return (0);
+}
diff --git a/tests/zfs-tests/include/commands.cfg b/tests/zfs-tests/include/commands.cfg
index 6e45d1ffc0af..d51518049e40 100644
--- a/tests/zfs-tests/include/commands.cfg
+++ b/tests/zfs-tests/include/commands.cfg
@@ -179,6 +179,7 @@ export ZFSTEST_FILES='badsend
     devname2devid
     dir_rd_update
     draid
+    file_append
     file_check
     file_trunc
     file_write
diff --git a/tests/zfs-tests/tests/Makefile.am b/tests/zfs-tests/tests/Makefile.am
index 355ad727dfe2..2202d9026787 100644
--- a/tests/zfs-tests/tests/Makefile.am
+++ b/tests/zfs-tests/tests/Makefile.am
@@ -385,6 +385,10 @@ nobase_dist_datadir_zfs_tests_tests_SCRIPTS += \
 	functional/alloc_class/alloc_class_013_pos.ksh \
 	functional/alloc_class/cleanup.ksh \
 	functional/alloc_class/setup.ksh \
+	functional/append/file_append.ksh \
+	functional/append/threadsappend_001_pos.ksh \
+	functional/append/cleanup.ksh \
+	functional/append/setup.ksh \
 	functional/arc/arcstats_runtime_tuning.ksh \
 	functional/arc/cleanup.ksh \
 	functional/arc/dbufstats_001_pos.ksh \
@@ -1842,9 +1846,6 @@ nobase_dist_datadir_zfs_tests_tests_SCRIPTS += \
 	functional/suid/suid_write_to_suid.ksh \
 	functional/suid/suid_write_to_suid_sgid.ksh \
 	functional/suid/suid_write_zil_replay.ksh \
-	functional/threadsappend/cleanup.ksh \
-	functional/threadsappend/setup.ksh \
-	functional/threadsappend/threadsappend_001_pos.ksh \
 	functional/trim/autotrim_config.ksh \
 	functional/trim/autotrim_integrity.ksh \
 	functional/trim/autotrim_trim_integrity.ksh \
diff --git a/tests/zfs-tests/tests/functional/threadsappend/cleanup.ksh b/tests/zfs-tests/tests/functional/append/cleanup.ksh
similarity index 81%
rename from tests/zfs-tests/tests/functional/threadsappend/cleanup.ksh
rename to tests/zfs-tests/tests/functional/append/cleanup.ksh
index 3166bd6ec16e..307feabd17c6 100755
--- a/tests/zfs-tests/tests/functional/threadsappend/cleanup.ksh
+++ b/tests/zfs-tests/tests/functional/append/cleanup.ksh
@@ -21,14 +21,9 @@
 #
 
 #
-# Copyright 2007 Sun Microsystems, Inc.  All rights reserved.
-# Use is subject to license terms.
+# Copyright (c) 2022 by Triad National Security, LCC
 #
 
-#
-# Copyright (c) 2013 by Delphix. All rights reserved.
-#
-
-. $STF_SUITE/include/libtest.shlib
+. ${STF_SUITE}/include/libtest.shlib
 
 default_cleanup
diff --git a/tests/zfs-tests/tests/functional/append/file_append.ksh b/tests/zfs-tests/tests/functional/append/file_append.ksh
new file mode 100755
index 000000000000..b40d10c05edb
--- /dev/null
+++ b/tests/zfs-tests/tests/functional/append/file_append.ksh
@@ -0,0 +1,73 @@
+#!/bin/ksh -p
+#
+# CDDL HEADER START
+#
+# The contents of this file are subject to the terms of the
+# Common Development and Distribution License (the "License").
+# You may not use this file except in compliance with the License.
+#
+# You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
+# or http://www.opensolaris.org/os/licensing.
+# See the License for the specific language governing permissions
+# and limitations under the License.
+#
+# When distributing Covered Code, include this CDDL HEADER in each
+# file and include the License file at usr/src/OPENSOLARIS.LICENSE.
+# If applicable, add the following below this CDDL HEADER, with the
+# fields enclosed by brackets "[]" replaced with your own identifying
+# information: Portions Copyright [yyyy] [name of copyright owner]
+#
+# CDDL HEADER END
+#
+
+#
+# Copyright (c) 2022 by Triad National Security, LCC
+#
+
+. $STF_SUITE/include/libtest.shlib
+
+#
+# DESCRIPTION:
+# Tests file offset using O_APPEND.
+#
+# STRATEGY:
+# 1. Open file using O_APPEND
+# 2. Write to the file using random number of blocks (1, 2, or 3)
+# 3. Verify that the file offset is correct using lseek after the write
+# 4. Repeat steps 2 and 3, 5 times
+# 5. Close the file.
+# 6. Repeat steps 1-5 but also open file with O_DIRECT
+#
+
+verify_runnable "global"
+
+log_assert "Ensure file offset is updated correctly when opened with O_APPEND"
+
+mntpt=$(get_prop mountpoint $TESTPOOL/$TESTFS)
+filename=$mntpt/append_file.txt
+bs=131072
+ITERATIONS=5
+expected=0
+
+# First test using buffered writes with O_APPEND
+for i in $(seq $ITERATIONS); do
+	num_blocks=$(random_int_between 1 3) 
+	expected=$((expected + ( bs * num_blocks)))
+	log_must file_append -f $filename -e $expected -b $bs -n $num_blocks
+	curr_offset=$expected
+done
+
+log_must rm -f $filename
+
+expected=0
+
+# Repeat same test using O_DIRECT writes with O_APPEND
+for i in $(seq $ITERATIONS); do
+	num_blocks=$(random_int_between 1 3) 
+	expected=$((expected + ( bs * num_blocks)))
+	log_must file_append -f $filename -e $expected -b $bs -n $num_blocks -d
+done
+
+log_must rm -f $filename
+
+log_pass "File offset updated correctly when opening a file with O_APPEND."
diff --git a/tests/zfs-tests/tests/functional/threadsappend/setup.ksh b/tests/zfs-tests/tests/functional/append/setup.ksh
similarity index 85%
rename from tests/zfs-tests/tests/functional/threadsappend/setup.ksh
rename to tests/zfs-tests/tests/functional/append/setup.ksh
index 4fc55cd47803..e692d7b1bc0c 100755
--- a/tests/zfs-tests/tests/functional/threadsappend/setup.ksh
+++ b/tests/zfs-tests/tests/functional/append/setup.ksh
@@ -21,12 +21,7 @@
 #
 
 #
-# Copyright 2007 Sun Microsystems, Inc.  All rights reserved.
-# Use is subject to license terms.
-#
-
-#
-# Copyright (c) 2013 by Delphix. All rights reserved.
+# Copyright (c) 2022 by Triad National Security, LCC
 #
 
 . $STF_SUITE/include/libtest.shlib
diff --git a/tests/zfs-tests/tests/functional/threadsappend/threadsappend_001_pos.ksh b/tests/zfs-tests/tests/functional/append/threadsappend_001_pos.ksh
similarity index 100%
rename from tests/zfs-tests/tests/functional/threadsappend/threadsappend_001_pos.ksh
rename to tests/zfs-tests/tests/functional/append/threadsappend_001_pos.ksh
diff --git a/tests/zfs-tests/tests/functional/threadsappend/.gitignore b/tests/zfs-tests/tests/functional/threadsappend/.gitignore
deleted file mode 100644
index 4c8c8cdf34c1..000000000000
--- a/tests/zfs-tests/tests/functional/threadsappend/.gitignore
+++ /dev/null
@@ -1 +0,0 @@
-/threadsappend