diff --git a/src/main.c b/src/main.c
index abf0d34..01c8d10 100644
--- a/src/main.c
+++ b/src/main.c
@@ -196,7 +196,7 @@
 #define MAIN int main(int argc, char **argv)
 #endif
 
-//TODO: Consider hashing strings for faster lookups
+//TODO: Consider hashing strings for faster lookups when parsing CLI
 //	Either SuperFastHash [1] or xxHash [2]
 //	[1] http://www.azillionmonkeys.com/qed/hash.html
 //	[2] https://github.com/Cyan4973/xxHash
diff --git a/src/vdisk.c b/src/vdisk.c
index 25f0d2b..8cf81a1 100644
--- a/src/vdisk.c
+++ b/src/vdisk.c
@@ -179,7 +179,7 @@
 			vd->u32blockcount = 1;
 		uint32_t bsize = vd->u32blockcount << 2;
 		if ((vd->u32block = malloc(bsize)) == NULL)
-			return vdisk_i_err(vd, VVD_EALLOC, LINE_BEFORE);
+			return vdisk_i_err(vd, VVD_ENOMEM, LINE_BEFORE);
 		vd->vdiv1.blockstotal = vd->u32blockcount;
 		vd->vdiv1.disksize = capacity;
 		switch (vd->vdiv1.type) {
@@ -189,7 +189,7 @@
 			break;
 		case VDI_DISK_FIXED:
 			if ((buffer = malloc(vd->vdiv1.blocksize)) == NULL)
-				return vdisk_i_err(vd, VVD_EALLOC, LINE_BEFORE);
+				return vdisk_i_err(vd, VVD_ENOMEM, LINE_BEFORE);
 			os_fseek(vd->fd, vd->vdiv1.offData, SEEK_SET);
 			for (size_t i = 0; i < vd->vdiv1.blockstotal; ++i) {
 				vd->u32block[i] = VDI_BLOCK_FREE;
diff --git a/src/vdisk.h b/src/vdisk.h
index 3e80d06..2435f93 100644
--- a/src/vdisk.h
+++ b/src/vdisk.h
@@ -23,6 +23,7 @@
 	VDISK_FORMAT_RAW	= 0xAAAAAAAA,	// Raw files and devices
 	VDISK_FORMAT_VDI	= 0x203C3C3C,	// "<<< " VirtualBox
 	VDISK_FORMAT_VMDK	= 0x564D444B,	// "VMDK" VMware
+	VDISK_FORMAT_VMDK_COW	= 0x44574F43,	// "COWD" VMware EXSi COW disk
 	VDISK_FORMAT_VHD	= 0x656E6F63,	// "cone" VirtualPC/Hyper-V
 	VDISK_FORMAT_VHDX	= 0x78646876,	// "vhdx" Hyper-V
 	VDISK_FORMAT_QED	= 0x00444551,	// "QED\0" QEMU Enhanced Disk
@@ -66,7 +67,7 @@
 	VVD_EOK	= 0,	// VDISK OK
 	VVD_EOS	= -2,	// OS/CRT related error
 	VVD_ENULL	= -3,	// Input pointer is NULL
-	VVD_EALLOC	= -4,	// Could not allocate memory
+	VVD_ENOMEM	= -4,	// Could not allocate memory
 	VVD_EVDFORMAT	= -10,	// Invalid VDISK format
 	VVD_EVDMAGIC	= -11,	// Invalid VDISK magic signature
 	VVD_EVDVERSION	= -12,	// Unsupported VDISK version (major)
@@ -218,7 +219,7 @@
  * 
  * \param vd VDISK structure
  * \param path OS string path
- * \param flags Flags
+ * \param flags Opening flags
  * 
  * \returns Exit status
  */
@@ -231,7 +232,7 @@
  * \param path OS string path
  * \param format Virtual disk format
  * \param capacity Virtual disk capacity
- * \param flags Flags
+ * \param flags Creation flags
  * 
  * \returns Exit status
  */
diff --git a/src/vdisk/bochs.h b/src/vdisk/bochs.h
index 29f1241..cad22c6 100644
--- a/src/vdisk/bochs.h
+++ b/src/vdisk/bochs.h
@@ -5,16 +5,20 @@
  * 
  * Little-endian
  * 
- * http://bochs.sourceforge.net/cgi-bin/topper.pl?name=New+Bochs+Documentation&url=http://bochs.sourceforge.net/doc/docbook/development/index.html
+ * http://bochs.sourceforge.net/doc/docbook/development/harddisk-redologs.html
  * §2.10
  */
 
 #include <stdint.h>
 
+static const uint32_t BOCHS_VERSION = 0x00020000;
+static const uint32_t BOCHS_V1 = 0x00010000;
+static const uint32_t BOCHS_UNALLOC = 0xffffffff;
+
 typedef struct {
 	char signacture[32];	// "Bochs Virtual HD Image"
 	char type[16];	// "Redolog"
-	char subtype[16];	// "Undoable", "Volatile", "Growing"
+	char subtype[16];	// "Undoable", "Volatile", "Growing", "vvfat"
 	uint32_t version;	// 0x00010000, 0x00020000
 	uint32_t hdrsize;	// 512
 } BOCH_HDR;
diff --git a/src/vdisk/qed.c b/src/vdisk/qed.c
index b39d6ef..56d04dd 100644
--- a/src/vdisk/qed.c
+++ b/src/vdisk/qed.c
@@ -31,9 +31,9 @@
 	uint32_t tablebits = fpow2(table_entries);
 
 	if ((vd->qed_L1 = malloc(table_size)) == NULL)
-		return vdisk_i_err(vd, VVD_EALLOC, LINE_BEFORE);
+		return vdisk_i_err(vd, VVD_ENOMEM, LINE_BEFORE);
 	if ((vd->qed_L2.offsets = malloc(table_size)) == NULL)
-		return vdisk_i_err(vd, VVD_EALLOC, LINE_BEFORE);
+		return vdisk_i_err(vd, VVD_ENOMEM, LINE_BEFORE);
 	if (os_fseek(vd->fd, vd->qed.cluster_size, SEEK_SET))
 		return vdisk_i_err(vd, VVD_EOS, LINE_BEFORE);
 	if (os_fread(vd->fd, vd->qed_L1, table_size))
diff --git a/src/vdisk/vdi.c b/src/vdisk/vdi.c
index 861b9e0..af2d796 100644
--- a/src/vdisk/vdi.c
+++ b/src/vdisk/vdi.c
@@ -63,7 +63,7 @@
 		return vdisk_i_err(vd, VVD_EOS, LINE_BEFORE);
 	int bsize = vd->vdiv1.blockstotal << 2; // * sizeof(u32)
 	if ((vd->u32block = malloc(bsize)) == NULL)
-		return vdisk_i_err(vd, VVD_EALLOC, LINE_BEFORE);
+		return vdisk_i_err(vd, VVD_ENOMEM, LINE_BEFORE);
 	if (os_fread(vd->fd, vd->u32block, bsize))
 		return vdisk_i_err(vd, VVD_EOS, LINE_BEFORE);
 
@@ -122,38 +122,37 @@
 	if (vd->vdiv1.type != VDI_DISK_DYN)
 		return vdisk_i_err(vd, VVD_EVDTYPE, LINE_BEFORE);
 
-	if (vd->vdiv1.blocksalloc == 0)
+	uint32_t *block2;	// back resolving array
+	uint32_t bk_alloc;	// blocks allocated
+
+	// 1. Allocate block array for back resolving.
+
+	uint64_t fsize;
+	if (os_fsize(vd->fd, &fsize))
+		return vdisk_i_err(vd, VVD_EVDMISC, LINE_BEFORE);
+
+	// This verifies that there are actually data blocks available
+	bk_alloc = (uint32_t)((fsize - vd->vdiv1.offData - vd->vdiv1.offBlocks) >> vd->vdi_blockshift);
+	if (bk_alloc == 0 || vd->vdiv1.blocksalloc == 0)
 		return 0;
 
-	uint32_t stat_unalloc = 0;	// unallocated blocks
-	uint32_t stat_occupied = 0;	// allocated blocks with data
-	uint32_t stat_zero = 0;	// blocks with no data inside
-	uint32_t stat_alloc = 0;	// allocated blocks
-
-	uint32_t *block2 = malloc(vd->vdiv1.blocksalloc << 2); // * 4
-	if (block2)
-		return vdisk_i_err(vd, VVD_EALLOC, LINE_BEFORE);
-	for (uint32_t i; i < vd->vdiv1.blocksalloc; ++i)
+	block2 = malloc(bk_alloc << 2);
+	if (block2 == NULL)
+		return vdisk_i_err(vd, VVD_ENOMEM, LINE_BEFORE);
+	for (uint32_t i; i < n; ++i)
 		block2[i] = VDI_BLOCK_FREE;
 
-/*	char strbsize[BINSTR_LENGTH];
-	bintostr(strbsize, vd->vdiv1.blocksize);
-	printf("vvd_compact: writing (%s/block, %u checks/%u bytes)...\n",
-		strbsize, (uint32_t)oblocksize, (uint32_t)sizeof(size_t));*/
-
 	uint32_t d = 0;
 	uint32_t i = 0;
 
-	// Check and fix allocation errors before compacting
+	// 2. Check and fix allocation errors before compacting
+
 	for (; i < vd->u32blockcount; ++i) {
 		uint32_t bi = vd->u32block[i]; // block index
 		if (bi >= VDI_BLOCK_FREE) {
-			++stat_unalloc;
 			continue;
 		}
 
-		if (cb) cb(VVD_NOTIF_VDISK_CURRENT_BLOCK, &i);
-
 		if (bi < vd->vdiv1.blocksalloc) {
 			if (vd->u32block[bi] == VDI_BLOCK_FREE) {
 				vd->u32block[bi] = i;
@@ -170,16 +169,21 @@
 			//vdisk_write_block_at(vd, buffer, i, d++);
 		}
 	}
-	// Find redundant information and update the block pointers accordingly
+
+	// 3. Find redundant information and update the block pointers accordingly
+
 	for (i = 0; i < vd->u32blockcount; ++i) {
 		uint32_t bi = vd->u32block[i]; // block index
 		if (bi >= VDI_BLOCK_FREE) {
-			++stat_unalloc;
 			continue;
 		}
 	}
-	// Fill bubbles with other data if available
-//		for (i = 0; o < vd->vdi.blocksalloc
+
+	// 4. Fill bubbles with other data if available
+
+//	for (i = 0; o < vd->vdi.blocksalloc
+
+	// 5. Update fields in-memory and on-disk
 
 	return 0;
 }
diff --git a/src/vdisk/vdi.h b/src/vdisk/vdi.h
index fffe413..9050307 100644
--- a/src/vdisk/vdi.h
+++ b/src/vdisk/vdi.h
@@ -14,13 +14,13 @@
  * Block marked as free is not allocated in image file, read from this
  * block may returns any random data.
  */
-static const uint32_t VDI_BLOCK_FREE = ~0;
+static const uint32_t VDI_BLOCK_FREE = 0xffffffff;
 
 /**
  * Block marked as zero is not allocated in image file, read from this
  * block returns zeroes.
  */
-static const uint32_t VDI_BLOCK_ZERO = ~1;
+static const uint32_t VDI_BLOCK_ZERO = 0xfffffffe;
 
 enum {
 	VDI_HEADER_MAGIC	= 0xBEDA107F,
@@ -93,4 +93,4 @@
 
 int vdisk_vdi_read_sector(struct VDISK *vd, void *buffer, uint64_t index);
 
-int vdisk_vdi_compact(struct VDISK *vd, void(*cb_progress)(uint32_t type, void *data));
+int vdisk_vdi_compact(struct VDISK *vd, void(*cb)(uint32_t type, void *data));
diff --git a/src/vdisk/vhd.c b/src/vdisk/vhd.c
index b65322b..8309650 100644
--- a/src/vdisk/vhd.c
+++ b/src/vdisk/vhd.c
@@ -101,7 +101,7 @@
 
 		int batsize = vd->u32blockcount << 2; // "* 4"
 		if ((vd->u32block = malloc(batsize)) == NULL)
-			return vdisk_i_err(vd, VVD_EALLOC, LINE_BEFORE);
+			return vdisk_i_err(vd, VVD_ENOMEM, LINE_BEFORE);
 		if (os_fread(vd->fd, vd->u32block, batsize))
 			return vdisk_i_err(vd, VVD_EOS, LINE_BEFORE);
 #if ENDIAN_LITTLE