diff --git a/include/spdk/reduce.h b/include/spdk/reduce.h
index 033462132..c7a8ebaa2 100644
--- a/include/spdk/reduce.h
+++ b/include/spdk/reduce.h
@@ -54,10 +54,18 @@ struct spdk_reduce_vol_params {
 	 */
 	uint32_t		backing_io_unit_size;
 
+	/**
+	 * Size in bytes of a logical block.  This is the unit in
+	 *  which users read or write data to the compressed volume.
+	 *  Must be greater than 0.
+	 */
+	uint32_t		logical_block_size;
+
 	/**
 	 * Size in bytes of a chunk on the compressed volume.  This
 	 *  is the unit in which data is compressed.  Must be an even
-	 *  multiple of backing_io_unit_size.  Must be greater than 0.
+	 *  multiple of backing_io_unit_size and logical_block_size.
+	 *  Must be greater than 0.
 	 */
 	uint32_t		chunk_size;
 
diff --git a/lib/reduce/reduce.c b/lib/reduce/reduce.c
index 8d23f9754..563e2dc81 100644
--- a/lib/reduce/reduce.c
+++ b/lib/reduce/reduce.c
@@ -57,7 +57,7 @@
 struct spdk_reduce_vol_superblock {
 	uint8_t				signature[8];
 	struct spdk_reduce_vol_params	params;
-	uint8_t				reserved[4056];
+	uint8_t				reserved[4048];
 };
 SPDK_STATIC_ASSERT(sizeof(struct spdk_reduce_vol_superblock) == 4096, "size incorrect");
 
@@ -82,6 +82,7 @@ struct spdk_reduce_vol_request {
 struct spdk_reduce_vol {
 	struct spdk_reduce_vol_params		params;
 	uint32_t				backing_io_units_per_chunk;
+	uint32_t				logical_blocks_per_chunk;
 	struct spdk_reduce_pm_file		pm_file;
 	struct spdk_reduce_backing_dev		*backing_dev;
 	struct spdk_reduce_vol_superblock	*backing_super;
@@ -149,7 +150,8 @@ _get_pm_total_chunks_size(uint64_t vol_size, uint64_t chunk_size, uint64_t backi
 static int
 _validate_vol_params(struct spdk_reduce_vol_params *params)
 {
-	if (params->vol_size == 0 || params->chunk_size == 0 || params->backing_io_unit_size == 0) {
+	if (params->vol_size == 0 || params->chunk_size == 0 ||
+	    params->backing_io_unit_size == 0 || params->logical_block_size == 0) {
 		return -EINVAL;
 	}
 
@@ -158,6 +160,11 @@ _validate_vol_params(struct spdk_reduce_vol_params *params)
 		return -EINVAL;
 	}
 
+	/* Chunk size must be an even multiple of the logical block size. */
+	if ((params->chunk_size % params->logical_block_size) != 0) {
+		return -1;
+	}
+
 	/* Volume size must be an even multiple of the chunk size. */
 	if ((params->vol_size % params->chunk_size) != 0) {
 		return -EINVAL;
@@ -448,6 +455,7 @@ spdk_reduce_vol_init(struct spdk_reduce_vol_params *params,
 	}
 
 	vol->backing_io_units_per_chunk = params->chunk_size / params->backing_io_unit_size;
+	vol->logical_blocks_per_chunk = params->chunk_size / params->logical_block_size;
 	memcpy(&vol->params, params, sizeof(*params));
 
 	rc = _allocate_bit_arrays(vol);
@@ -515,6 +523,7 @@ _load_read_super_and_path_cpl(void *cb_arg, int ziperrno)
 
 	memcpy(&vol->params, &vol->backing_super->params, sizeof(vol->params));
 	vol->backing_io_units_per_chunk = vol->params.chunk_size / vol->params.backing_io_unit_size;
+	vol->logical_blocks_per_chunk = vol->params.chunk_size / vol->params.logical_block_size;
 
 	rc = _allocate_bit_arrays(vol);
 	if (rc != 0) {
diff --git a/test/unit/lib/reduce/reduce.c/reduce_ut.c b/test/unit/lib/reduce/reduce.c/reduce_ut.c
index fb21ec829..2525d0992 100644
--- a/test/unit/lib/reduce/reduce.c/reduce_ut.c
+++ b/test/unit/lib/reduce/reduce.c/reduce_ut.c
@@ -123,6 +123,7 @@ get_backing_device_size(void)
 	params.vol_size = 0;
 	params.chunk_size = 0;
 	params.backing_io_unit_size = 0;
+	params.logical_block_size = 512;
 	CU_ASSERT(spdk_reduce_get_backing_device_size(&params) == -EINVAL);
 
 	/*
@@ -223,6 +224,7 @@ init_failure(void)
 	params.vol_size = 1024 * 1024; /* 1MB */
 	params.chunk_size = 16 * 1024;
 	params.backing_io_unit_size = backing_dev.blocklen;
+	params.logical_block_size = 512;
 
 	/* backing_dev and pm_file have an invalid size.  This should fail. */
 	g_vol = NULL;
@@ -329,6 +331,7 @@ init_md(void)
 	params.vol_size = 1024 * 1024; /* 1MB */
 	params.chunk_size = 16 * 1024;
 	params.backing_io_unit_size = 512;
+	params.logical_block_size = 512;
 
 	backing_dev_init(&backing_dev, &params);
 
@@ -380,6 +383,7 @@ init_backing_dev(void)
 	params.vol_size = 1024 * 1024; /* 1MB */
 	params.chunk_size = 16 * 1024;
 	params.backing_io_unit_size = 512;
+	params.logical_block_size = 512;
 	spdk_uuid_generate(&params.uuid);
 
 	backing_dev_init(&backing_dev, &params);
@@ -423,6 +427,7 @@ load(void)
 	params.vol_size = 1024 * 1024; /* 1MB */
 	params.chunk_size = 16 * 1024;
 	params.backing_io_unit_size = 512;
+	params.logical_block_size = 512;
 	spdk_uuid_generate(&params.uuid);
 
 	backing_dev_init(&backing_dev, &params);