diff --git a/raid.c b/raid.c
index bd470a85..e584d61e 100644
--- a/raid.c
+++ b/raid.c
@@ -1232,8 +1232,8 @@ void raid_gen(unsigned level, unsigned char** buffer, unsigned diskmax, unsigned
  * This method is also the same used by ZFS to implement its RAIDTP
  * support.
  *
- * Note that the same extension is not possible for Quad Parity because
- * in the approach used in the paper we don't have the guarantee to always have
+ * To support RAIDQP (Quad Parity) we go futher using also the parity generator "8".
+ * Note that in this case we don't have the guarantee to always have
  * a system of independent linear equations, and for Quad Parity in some cases
  * the system is not solvable.
  *
@@ -1258,18 +1258,18 @@ void raid_gen(unsigned level, unsigned char** buffer, unsigned diskmax, unsigned
  * Q = sum(2^i * Di) 0<=i<n
  * R = sum(4^i * Di) 0<=i<n
  *
- * To recover from a failure of three disks at indes x,y,z,
+ * To recover from a failure of three disks at indexes x,y,z,
  * with 0<=x<y<z<n, we compute the syndromes of the available disks:
  *
- * Pxyz = sum(Di) 0<=i<n,i!=x,i!=y,i!=z
- * Qxyz = sum(2^i * Di) 0<=i<n,i!=x,i!=y,i!=z
- * Rxyz = sum(4^i * Di) 0<=i<n,i!=x,i!=y,i!=z
+ * Pa = sum(Di) 0<=i<n,i!=x,i!=y,i!=z
+ * Qa = sum(2^i * Di) 0<=i<n,i!=x,i!=y,i!=z
+ * Ra = sum(4^i * Di) 0<=i<n,i!=x,i!=y,i!=z
  *
  * and if we define:
  *
- * Pd = Pxyz + P
- * Qd = Qxyz + Q
- * Rd = Rxyz + R
+ * Pd = Pa + P
+ * Qd = Qa + Q
+ * Rd = Ra + R
  *
  * we can sum these two set equations, obtaining:
  *
@@ -1277,27 +1277,31 @@ void raid_gen(unsigned level, unsigned char** buffer, unsigned diskmax, unsigned
  * Qd = 2^x * Dx + 2^y * Dy + 2^z * Dz
  * Rd = 4^x * Dx + 4^y * Dy + 4^z * Dz
  *
- * A linear system of three equations solvable by substitution on Dx, Dy and Dz,
- * because all the others variables are known and the equations are independent
- * for any 0<=x<y<z<255.
- * We can prove that the equations are independent by brute-force, trying all the
- * possible combinations of x,y,z.
+ * A linear system always solvable because the coefficients matrix is always
+ * not singular, including all its submatrix.
+ * We can prove that by brute-force, trying all the possible combinations
+ * of x,y,z with 0<=x<y<z<255.
  *
  * The other recovering cases are a simplification of the general one,
  * with some equations or addends removed.
  *
- * We have in total 7 different recovering strategies:
+ * For Quad Parity we follow the same method starting with:
  *
- * RAID5 - Dx recovered with P
- * RAID6 - Dx recovered with Q
- * RAID6 - Dx and Dy recovered with P,Q
- * RAIDTP - Dx recovered with R
- * RAIDTP - Dx,Dy recovered with P,R
- * RAIDTP - Dx,Dy recovered with Q,R
- * RAIDTP - Dx,Dy,Dz recovered with P,Q,R
+ * P = sum(Di) 0<=i<n
+ * Q = sum(2^i * Di) 0<=i<n
+ * R = sum(4^i * Di) 0<=i<n
+ * S = sum(8^i * Di) 0<=i<n
  *
- * each one implemented in a different function using linear system
- * of equations with a different solution.
+ * obtaining:
+ *
+ * Pd =       Dx +       Dy +       Dz +       Dv
+ * Qd = 2^x * Dx + 2^y * Dy + 2^z * Dz + 2^v * Dv
+ * Rd = 4^x * Dx + 4^y * Dy + 4^z * Dz + 4^v * Dv
+ * Sd = 8^x * Dx + 8^y * Dy + 8^z * Dz + 8^v * Dv
+ *
+ * In this case the coefficients matrix and all its submatrix are not singular
+ * only with up to 21 data disk (0<=x<y<z<v<21 with GF primitive poly 285).
+ * Note that the cases failing with 22 data disk are some matrix 3x3.
  *
  * References:
  * [1] Anvin, "The mathematics of RAID-6", 2004
@@ -1390,7 +1394,9 @@ static inline const unsigned char* table(unsigned char a)
 	return gfmul[a];
 }
 
-/*
+/**
+ * Recover failure of one data block for RAID5.
+ *
  * Starting from the equation:
  *
  * Pd = Dx
@@ -1399,7 +1405,7 @@ static inline const unsigned char* table(unsigned char a)
  *
  * Dx = Pd (this one is easy :D)
  */
-void raid5_recov_data(unsigned char** dptrs, unsigned diskmax, unsigned size, int x)
+static void raid5_recov_data(unsigned char** dptrs, unsigned diskmax, unsigned size, int x)
 {
 	unsigned char* p;
 	unsigned char* dp;
@@ -1418,7 +1424,9 @@ void raid5_recov_data(unsigned char** dptrs, unsigned diskmax, unsigned size, in
 	dptrs[diskmax] = p;
 }
 
-/*
+/**
+ * Recover failure of two data blocks for RAID6.
+ *
  * Starting from the equations:
  *
  * Pd = Dx + Dy
@@ -1439,7 +1447,7 @@ void raid5_recov_data(unsigned char** dptrs, unsigned diskmax, unsigned size, in
  *
  * That are always satisfied for any 0<=x<y<255.
  */
-void raid6_recov_2data(unsigned char** dptrs, unsigned diskmax, unsigned size, int x, int y, unsigned char* zero)
+static void raid6_recov_2data(unsigned char** dptrs, unsigned diskmax, unsigned size, int x, int y, unsigned char* zero)
 {
 	unsigned char* p;
 	unsigned char* dp;
@@ -1498,120 +1506,9 @@ void raid6_recov_2data(unsigned char** dptrs, unsigned diskmax, unsigned size, i
 	}
 }
 
-/*
- * Starting from the equations:
+/**
+ * Recover failure of two data blocks without Q for RAIDTP.
  *
- * Qd = 2^x * Dx
- *
- * and solving we get:
- *
- * Dx = 2^(-x) * Qd
- *
- * with conditions:
- *
- * 2^x != 0
- *
- * That are always satisfied for any 0<=x<y<255.
- */
-void raid6_recov_datap(unsigned char** dptrs, unsigned diskmax, unsigned size, int x, unsigned char* zero)
-{
-	unsigned char* q;
-	unsigned char* dq;
-	const unsigned char* qxmul; /* Q multiplier to compute Dx */
-
-	q = dptrs[diskmax+1];
-
-	/* compute syndrome with zero for the missing data page */
-	/* use the dead data page as temporary storage for delta q */
-	dq = dptrs[x];
-	dptrs[x] = zero;
-	dptrs[diskmax+1] = dq;
-
-	raid6_gen(dptrs, diskmax, size);
-
-	/* restore pointers */
-	dptrs[x] = dq;
-	dptrs[diskmax+1] = q;
-
-	/* select tables */
-	qxmul = table( inv(pow2(x)) );
-
-	while (size--) {
-		/* delta */
-		unsigned char Qd = *q ^ *dq;
-
-		/* addends to reconstruct Dx */
-		unsigned char qam = qxmul[Qd];
-
-		/* reconstruct Dx */
-		unsigned char Dx = qam;
-
-		/* set */
-		*dq = Dx;
-
-		++q;
-		++dq;
-	}
-}
-
-/*
- * Starting from the equation:
- *
- * Rd = 4^x * Dx
- *
- * and solving we get:
- *
- * Dx = 4^(-x) * Rd
- *
- * with conditions:
- *
- * 4^x != 0
- *
- * That are always satisfied for any 0<=x<y<255.
- *
- */
-void raidTP_recov_datapq(unsigned char** dptrs, unsigned diskmax, unsigned size, int x, unsigned char* zero)
-{
-	unsigned char* r;
-	unsigned char* dr;
-	const unsigned char* rxmul; /* R multiplier to compute Dx */
-
-	r = dptrs[diskmax+2];
-
-	/* compute syndrome with zero for the missing data page */
-	/* use the dead data page as temporary storage for delta r */
-	dr = dptrs[x];
-	dptrs[x] = zero;
-	dptrs[diskmax+2] = dr;
-
-	raidTP_gen(dptrs, diskmax, size);
-
-	/* restore pointers */
-	dptrs[x] = dr;
-	dptrs[diskmax+2] = r;
-
-	/* select tables */
-	rxmul = table( inv(pow4(x)) );
-
-	while (size--) {
-		/* delta */
-		unsigned char Rd = *r ^ *dr;
-
-		/* addends to reconstruct Dx */
-		unsigned char rxm = rxmul[Rd];
-
-		/* reconstruct Dx */
-		unsigned char Dx = rxm;
-
-		/* set */
-		*dr = Dx;
-
-		++r;
-		++dr;
-	}
-}
-
-/*
  * Starting from the equations:
  *
  * Pd = Dx + Dy
@@ -1632,7 +1529,7 @@ void raidTP_recov_datapq(unsigned char** dptrs, unsigned diskmax, unsigned size,
  *
  * That are always satisfied for any 0<=x<y<255.
  */
-void raidTP_recov_2dataq(unsigned char** dptrs, unsigned diskmax, unsigned size, int x, int y, unsigned char* zero)
+static void raidTP_recov_2dataq(unsigned char** dptrs, unsigned diskmax, unsigned size, int x, int y, unsigned char* zero)
 {
 	unsigned char* p;
 	unsigned char* dp;
@@ -1693,7 +1590,9 @@ void raidTP_recov_2dataq(unsigned char** dptrs, unsigned diskmax, unsigned size,
 	}
 }
 
-/*
+/**
+ * Recover failure of two data blocks without P for RAIDTP.
+ *
  * Starting from the equations:
  *
  * Qd = 2^x * Dx + 2^y * Dy
@@ -1715,7 +1614,7 @@ void raidTP_recov_2dataq(unsigned char** dptrs, unsigned diskmax, unsigned size,
  *
  * That are always satisfied for any 0<=x<y<255.
  */
-void raidTP_recov_2datap(unsigned char** dptrs, unsigned diskmax, unsigned size, int x, int y, unsigned char* zero)
+static void raidTP_recov_2datap(unsigned char** dptrs, unsigned diskmax, unsigned size, int x, int y, unsigned char* zero)
 {
 	unsigned char* q;
 	unsigned char* dq;
@@ -1784,7 +1683,9 @@ void raidTP_recov_2datap(unsigned char** dptrs, unsigned diskmax, unsigned size,
 	}
 }
 
-/*
+/**
+ * Recover failure of three data blocks for RAIDTP.
+ *
  * Starting from the equations:
  *
  * Pd = Dx + Dy + Dz
@@ -1817,7 +1718,7 @@ void raidTP_recov_2datap(unsigned char** dptrs, unsigned diskmax, unsigned size,
  *
  * That are always satisfied for any 0<=x<y<z<255.
  */
-void raidTP_recov_3data(unsigned char** dptrs, unsigned diskmax, unsigned size, int x, int y, int z, unsigned char* zero)
+static void raidTP_recov_3data(unsigned char** dptrs, unsigned diskmax, unsigned size, int x, int y, int z, unsigned char* zero)
 {
 	unsigned char* p;
 	unsigned char* dp;
@@ -1972,18 +1873,20 @@ static void invert(unsigned char* M, unsigned char* V, unsigned n)
 	}
 }
 
-/*
+/**
+ * Recover failure of one data block x using parity i for any RAID level.
+ *
  * Starting from the equation:
  *
- * Sd = 2^i^x * Dx
+ * Sd = (2^i)^x * Dx
  *
  * and solving we get:
  *
- * Dx = 2^i^(-x) * Sd
+ * Dx = (2^i)^(-x) * Sd
  *
  * with conditions:
  *
- * 2^i^x != 0
+ * (2^i)^x != 0
  *
  * That are always satisfied for any 0<=x<y<255.
  */
@@ -1993,9 +1896,11 @@ void raid_recov_1data(unsigned char** dptrs, unsigned diskmax, unsigned size, in
 	unsigned char* dp;
 	const unsigned char* pxmul; /* P multiplier to compute Dx */
 
-	/* if i is P use the fast one */
-	if (i == 0)
+	/* if it's RAID5 uses the dedicated and faster function */
+	if (i == 0) {
 		raid5_recov_data(dptrs, diskmax, size, x);
+		return;
+	}
 
 	p = dptrs[diskmax+i];
 
@@ -2032,11 +1937,13 @@ void raid_recov_1data(unsigned char** dptrs, unsigned diskmax, unsigned size, in
 	}
 }
 
-/*
+/**
+ * Recover failure of two data blocks x,y using parity i,j for any RAID level.
+ *
  * Starting from the equations:
  *
- * Pd = 2^i^x * Dx + 2^i^y * Dy
- * Qd = 2^j^x * Dx + 2^j^y * Dy
+ * Pd = (2^i)^x * Dx + (2^i)^y * Dy
+ * Qd = (2^j)^x * Dx + (2^j)^y * Dy
  *
  * we solve inverting the coefficients matrix.
  */
@@ -2054,6 +1961,22 @@ void raid_recov_2data(unsigned char** dptrs, unsigned diskmax, unsigned size, in
 	unsigned char V[2*2];
 	unsigned n = 2;
 
+	/* if it's RAID6 uses the dedicated and faster function */
+	if (i == 0 && j == 1) {
+		raid6_recov_2data(dptrs, diskmax, size, x, y, zero);
+		return;
+	}
+	/* if it's RAIDTP uses the dedicated and faster function */
+	if (i == 0 && j == 2) {
+		raidTP_recov_2dataq(dptrs, diskmax, size, x, y, zero);
+		return;
+	}
+	/* if it's RAIDTP uses the dedicated and faster function */
+	if (i == 1 && j == 2) {
+		raidTP_recov_2datap(dptrs, diskmax, size, x, y, zero);
+		return;
+	}
+
 	p = dptrs[diskmax+i];
 	q = dptrs[diskmax+j];
 
@@ -2127,12 +2050,14 @@ void raid_recov_2data(unsigned char** dptrs, unsigned diskmax, unsigned size, in
 	}
 }
 
-/*
+/**
+ * Recover failure of three data blocks x,y,z using parity i,j,k for any RAID level.
+ *
  * Starting from the equations:
  *
- * Pd = 2^i^x * Dx + 2^i^y * Dy + 2^i^z * Dz
- * Qd = 2^j^x * Dx + 2^j^y * Dy + 2^j^z * Dz
- * Rd = 2^k^x * Dx + 2^k^y * Dy + 2^k^z * Dz
+ * Pd = (2^i)^x * Dx + (2^i)^y * Dy + (2^i)^z * Dz
+ * Qd = (2^j)^x * Dx + (2^j)^y * Dy + (2^j)^z * Dz
+ * Rd = (2^k)^x * Dx + (2^k)^y * Dy + (2^k)^z * Dz
  *
  * we solve inverting the coefficients matrix.
  */
@@ -2157,6 +2082,12 @@ void raid_recov_3data(unsigned char** dptrs, unsigned diskmax, unsigned size, in
 	unsigned char V[3*3];
 	unsigned n = 3;
 
+	/* if it's RAIDTP uses the dedicated and faster function */
+	if (i == 0 && j == 1 && k == 2) {
+		raidTP_recov_3data(dptrs, diskmax, size, x, y, z, zero);
+		return;
+	}
+
 	p = dptrs[diskmax+i];
 	q = dptrs[diskmax+j];
 	r = dptrs[diskmax+k];
@@ -2260,13 +2191,15 @@ void raid_recov_3data(unsigned char** dptrs, unsigned diskmax, unsigned size, in
 	}
 }
 
-/*
+/**
+ * Recover failure of four data blocks x,y,z,v using parity i,j,k,l for any RAID level.
+ *
  * Starting from the equations:
  *
- * Pd = 2^i^x * Dx + 2^i^y * Dy + 2^i^z * Dz + 2^i^v * Dv
- * Qd = 2^j^x * Dx + 2^j^y * Dy + 2^j^z * Dz + 2^j^v * Dv
- * Rd = 2^k^x * Dx + 2^k^y * Dy + 2^k^z * Dz + 2^k^v * Dv
- * Sd = 2^l^x * Dx + 2^l^y * Dy + 2^l^z * Dz + 2^l^v * Dv
+ * Pd = (2^i)^x * Dx + (2^i)^y * Dy + (2^i)^z * Dz + (2^i)^v * Dv
+ * Qd = (2^j)^x * Dx + (2^j)^y * Dy + (2^j)^z * Dz + (2^j)^v * Dv
+ * Rd = (2^k)^x * Dx + (2^k)^y * Dy + (2^k)^z * Dz + (2^k)^v * Dv
+ * Sd = (2^l)^x * Dx + (2^l)^y * Dy + (2^l)^z * Dz + (2^l)^v * Dv
  *
  * we solve inverting the coefficients matrix.
  */
diff --git a/raid.h b/raid.h
index 120efe68..14fb1194 100644
--- a/raid.h
+++ b/raid.h
@@ -21,50 +21,16 @@
 /****************************************************************************/
 /* raid */
 
+/**
+ * Max number of data disks for quad parity.
+ */
+#define RAID_QUAD_DATA_LIMIT 21
+
 /**
  * Syndrome computation.
  */
 void raid_gen(unsigned level, unsigned char** buffer, unsigned diskmax, unsigned size);
 
-/*
- * Recover failure of one data block.
- */
-void raid5_recov_data(unsigned char** dptrs, unsigned diskmax, unsigned size, int faila);
-
-/*
- * Recover two failed data blocks.
- */
-void raid6_recov_2data(unsigned char** dptrs, unsigned diskmax, unsigned size, int faila, int failb, unsigned char* zero);
-
-/*
- * Recover failure of one data block ignoring P.
- * Note that P content is not recovered.
- */
-void raid6_recov_datap(unsigned char** dptrs, unsigned diskmax, unsigned size, int faila, unsigned char* zero);
-
-/*
- * Recover failure of one data block ignoring P and Q.
- * Note that P and Q content is not recovered.
- */
-void raidTP_recov_datapq(unsigned char** dptrs, unsigned diskmax, unsigned size, int faila, unsigned char* zero);
-
-/*
- * Recover failure of two data blocks ignoring P.
- * Note that P content is not recovered.
- */
-void raidTP_recov_2datap(unsigned char** dptrs, unsigned diskmax, unsigned size, int faila, int failb, unsigned char* zero);
-
-/*
- * Recover failure of two data blocks ignoring Q.
- * Note that Q content is not recovered.
- */
-void raidTP_recov_2dataq(unsigned char** dptrs, unsigned diskmax, unsigned size, int faila, int failb, unsigned char* zero);
-
-/*
- * Recover failure of three data blocks.
- */
-void raidTP_recov_3data(unsigned char** dptrs, unsigned diskmax, unsigned size, int faila, int failb, int failc, unsigned char* zero);
-
 /*
  * Recover failure of one data block x using parity i.
  */
diff --git a/selftest.c b/selftest.c
index 01dd4ab3..3e2204b3 100644
--- a/selftest.c
+++ b/selftest.c
@@ -20,6 +20,8 @@
 #include "snapraid.h"
 #include "util.h"
 #include "raid.h"
+#include "elem.h"
+#include "state.h"
 
 struct hash_test_vector {
 	const char* data;
@@ -43,338 +45,7 @@ static struct hash_test_vector TEST_SPOOKY2[] = {
 { 0, 0, { 0 } }
 };
 
-static void raid5test(unsigned diskmax, unsigned block_size)
-{
-	void* buffer_alloc;
-	unsigned char** buffer;
-	unsigned char* buffer_test;
-	unsigned buffermax;
-	unsigned i, j;
-
-	buffermax = diskmax + 1 + 1;
-
-	buffer = malloc_nofail_vector_align(buffermax, block_size, &buffer_alloc);
-
-	buffer_test = buffer[buffermax-1];
-
-	/* fill with random */
-	for(i=0;i<diskmax;++i) {
-		for(j=0;j<block_size;++j)
-			buffer[i][j] = rand();
-	}
-
-	/* compute the parity */
-	raid_gen(1, buffer, diskmax, block_size);
-
-	for(i=0;i<diskmax;++i) {
-		unsigned char* a;
-
-		/* save */
-		a = buffer[i];
-
-		/* damage */
-		buffer[i] = buffer_test;
-
-		/* recover */
-		raid5_recov_data(buffer, diskmax, block_size, i);
-
-		/* restore */
-		buffer[i] = a;
-
-		/* check */
-		if (memcmp(buffer_test, buffer[i], block_size) != 0) {
-			fprintf(stderr, "Failed RAID5 test\n");
-			exit(EXIT_FAILURE);
-		}
-	}
-
-	free(buffer_alloc);
-	free(buffer);
-}
-
-static void raid6test(unsigned diskmax, unsigned block_size)
-{
-	void* buffer_alloc;
-	unsigned char** buffer;
-	unsigned char* buffer_test0;
-	unsigned char* buffer_test1;
-	unsigned char* buffer_zero;
-	unsigned char* buffer_bad;
-	unsigned buffermax;
-	unsigned i, j;
-
-	buffermax = diskmax + 2 + 2 + 1 + 1;
-
-	buffer = malloc_nofail_vector_align(buffermax, block_size, &buffer_alloc);
-
-	buffer_test0 = buffer[buffermax-4];
-	buffer_test1 = buffer[buffermax-3];
-	buffer_zero = buffer[buffermax-2];
-	buffer_bad = buffer[buffermax-1];
-	memset(buffer_zero, 0, block_size);
-	memset(buffer_bad, 0xA5, block_size);
-
-	/* fill with random */
-	for(i=0;i<diskmax;++i) {
-		for(j=0;j<block_size;++j)
-			buffer[i][j] = rand();
-	}
-
-	/* compute the parity */
-	raid_gen(2, buffer, diskmax, block_size);
-
-	/* check 2data */
-	for(i=0;i<diskmax;++i) {
-		for(j=i+1;j<diskmax;++j) {
-			unsigned char* a;
-			unsigned char* b;
-
-			/* save */
-			a = buffer[i];
-			b = buffer[j];
-
-			/* damage */
-			buffer[i] = buffer_test0;
-			buffer[j] = buffer_test1;
-
-			/* recover */
-			raid6_recov_2data(buffer, diskmax, block_size, i, j, buffer_zero);
-
-			/* restore */
-			buffer[i] = a;
-			buffer[j] = b;
-
-			/* check */
-			if (memcmp(buffer_test0, buffer[i], block_size) != 0
-				|| memcmp(buffer_test1, buffer[j], block_size) != 0
-			) {
-				fprintf(stderr, "Failed RAID6 test\n");
-				exit(EXIT_FAILURE);
-			}
-		}
-	}
-
-	/* check datap */
-	for(i=0;i<diskmax;++i) {
-		unsigned char* a;
-		unsigned char* p;
-
-		/* other is p */
-		j = diskmax;
-
-		/* save */
-		a = buffer[i];
-		p = buffer[j];
-
-		/* damage */
-		buffer[i] = buffer_test0;
-		buffer[j] = buffer_bad;
-
-		/* recover */
-		raid6_recov_datap(buffer, diskmax, block_size, i, buffer_zero);
-
-		/* restore */
-		buffer[i] = a;
-		buffer[j] = p;
-
-		/* check */
-		if (memcmp(buffer_test0, buffer[i], block_size) != 0) {
-			fprintf(stderr, "Failed RAID6 test\n");
-			exit(EXIT_FAILURE);
-		}
-	}
-
-	free(buffer_alloc);
-	free(buffer);
-}
-
-static void raidTPtest(unsigned diskmax, unsigned block_size)
-{
-	void* buffer_alloc;
-	unsigned char** buffer;
-	unsigned char* buffer_test0;
-	unsigned char* buffer_test1;
-	unsigned char* buffer_test2;
-	unsigned char* buffer_zero;
-	unsigned char* buffer_bad;
-	unsigned buffermax;
-	unsigned i, j, k;
-
-	buffermax = diskmax + 3 + 3 + 1 + 1;
-
-	buffer = malloc_nofail_vector_align(buffermax, block_size, &buffer_alloc);
-
-	buffer_test0 = buffer[buffermax-5];
-	buffer_test1 = buffer[buffermax-4];
-	buffer_test2 = buffer[buffermax-3];
-	buffer_zero = buffer[buffermax-2];
-	buffer_bad = buffer[buffermax-1];
-	memset(buffer_zero, 0, block_size);
-	memset(buffer_bad, 0xA5, block_size);
-
-	/* fill with random */
-	for(i=0;i<diskmax;++i) {
-		for(j=0;j<block_size;++j)
-			buffer[i][j] = rand();
-	}
-
-	/* compute the parity */
-	raid_gen(3, buffer, diskmax, block_size);
-
-	/* check 3data */
-	for(i=0;i<diskmax;++i) {
-		for(j=i+1;j<diskmax;++j) {
-			for(k=j+1;k<diskmax;++k) {
-				unsigned char* a;
-				unsigned char* b;
-				unsigned char* c;
-
-				/* save */
-				a = buffer[i];
-				b = buffer[j];
-				c = buffer[k];
-
-				/* damage */
-				buffer[i] = buffer_test0;
-				buffer[j] = buffer_test1;
-				buffer[k] = buffer_test2;
-
-				/* recover */
-				raidTP_recov_3data(buffer, diskmax, block_size, i, j, k, buffer_zero);
-
-				/* restore */
-				buffer[i] = a;
-				buffer[j] = b;
-				buffer[k] = c;
-
-				/* check */
-				if (memcmp(buffer_test0, buffer[i], block_size) != 0
-					|| memcmp(buffer_test1, buffer[j], block_size) != 0
-					|| memcmp(buffer_test2, buffer[k], block_size) != 0
-				) {
-					fprintf(stderr, "Failed RAIDTP test\n");
-					exit(EXIT_FAILURE);
-				}
-			}
-		}
-	}
-
-	/* check 2dataq */
-	for(i=0;i<diskmax;++i) {
-		for(j=i+1;j<diskmax;++j) {
-			unsigned char* a;
-			unsigned char* b;
-			unsigned char* q;
-
-			/* other is q */
-			k = diskmax + 1;
-
-			/* save */
-			a = buffer[i];
-			b = buffer[j];
-			q = buffer[k];
-
-			/* damage */
-			buffer[i] = buffer_test0;
-			buffer[j] = buffer_test1;
-			buffer[k] = buffer_bad;
-
-			/* recover */
-			raidTP_recov_2dataq(buffer, diskmax, block_size, i, j, buffer_zero);
-
-			/* restore */
-			buffer[i] = a;
-			buffer[j] = b;
-			buffer[k] = q;
-
-			/* check */
-			if (memcmp(buffer_test0, buffer[i], block_size) != 0
-				|| memcmp(buffer_test1, buffer[j], block_size) != 0
-			) {
-				fprintf(stderr, "Failed RAIDTP test\n");
-				exit(EXIT_FAILURE);
-			}
-		}
-	}
-
-	/* check 2datap */
-	for(i=0;i<diskmax;++i) {
-		for(j=i+1;j<diskmax;++j) {
-			unsigned char* a;
-			unsigned char* b;
-			unsigned char* p;
-
-			/* other is p */
-			k = diskmax;
-
-			/* save */
-			a = buffer[i];
-			b = buffer[j];
-			p = buffer[k];
-
-			/* damage */
-			buffer[i] = buffer_test0;
-			buffer[j] = buffer_test1;
-			buffer[k] = buffer_bad;
-
-			/* recover */
-			raidTP_recov_2datap(buffer, diskmax, block_size, i, j, buffer_zero);
-
-			/* restore */
-			buffer[i] = a;
-			buffer[j] = b;
-			buffer[k] = p;
-
-			/* check */
-			if (memcmp(buffer_test0, buffer[i], block_size) != 0
-				|| memcmp(buffer_test1, buffer[j], block_size) != 0
-			) {
-				fprintf(stderr, "Failed RAIDTP test\n");
-				exit(EXIT_FAILURE);
-			}
-		}
-	}
-
-	/* check datapq */
-	for(i=0;i<diskmax;++i) {
-		unsigned char* a;
-		unsigned char* p;
-		unsigned char* q;
-
-		/* others are p,q */
-		j = diskmax;
-		k = diskmax + 1;
-
-		/* save */
-		a = buffer[i];
-		p = buffer[j];
-		q = buffer[k];
-
-		/* damage */
-		buffer[i] = buffer_test0;
-		buffer[j] = buffer_bad;
-		buffer[k] = buffer_bad;
-
-		/* recover */
-		raidTP_recov_datapq(buffer, diskmax, block_size, i, buffer_zero);
-
-		/* restore */
-		buffer[i] = a;
-		buffer[j] = p;
-		buffer[k] = q;
-
-		/* check */
-		if (memcmp(buffer_test0, buffer[i], block_size) != 0) {
-			fprintf(stderr, "Failed RAIDTP test\n");
-			exit(EXIT_FAILURE);
-		}
-	}
-
-	free(buffer_alloc);
-	free(buffer);
-}
-
-static void raidQPtest(unsigned diskmax, unsigned block_size)
+static void raidtest(unsigned diskmax, unsigned block_size)
 {
 	void* buffer_alloc;
 	unsigned char** buffer;
@@ -391,7 +62,7 @@ static void raidQPtest(unsigned diskmax, unsigned block_size)
 	struct combo1 {
 		int ignore[3];
 		int use;
-	} COMBO1[4] = {
+	} COMBO1[] = {
 		{ { 1, 2, 3 }, 0 },
 		{ { 0, 2, 3 }, 1 },
 		{ { 0, 1, 3 }, 2 },
@@ -401,7 +72,7 @@ static void raidQPtest(unsigned diskmax, unsigned block_size)
 	struct combo2 {
 		int ignore[2];
 		int use[2];
-	} COMBO2[6] = {
+	} COMBO2[] = {
 		{ { 0, 1 }, { 2, 3 } },
 		{ { 0, 2 }, { 1, 3 } },
 		{ { 0, 3 }, { 1, 2 } },
@@ -413,14 +84,14 @@ static void raidQPtest(unsigned diskmax, unsigned block_size)
 	struct combo3 {
 		int ignore;
 		int use[3];
-	} COMBO3[4] = {
+	} COMBO3[] = {
 		{ 0, { 1, 2, 3 } },
 		{ 1, { 0, 2, 3 } },
 		{ 2, { 0, 1, 3 } },
 		{ 3, { 0, 1, 2 } }
 	};
 
-	buffermax = diskmax + 4 + 4 + 1 + 1;
+	buffermax = diskmax + LEV_MAX * 2 + 1 + 1;
 
 	buffer = malloc_nofail_vector_align(buffermax, block_size, &buffer_alloc);
 
@@ -440,7 +111,7 @@ static void raidQPtest(unsigned diskmax, unsigned block_size)
 	}
 
 	/* compute the parity */
-	raid_gen(4, buffer, diskmax, block_size);
+	raid_gen(LEV_MAX, buffer, diskmax, block_size);
 
 	/* check 4data */
 	for(i=0;i<diskmax;++i) {
@@ -473,7 +144,7 @@ static void raidQPtest(unsigned diskmax, unsigned block_size)
 						|| memcmp(buffer_test2, c, block_size) != 0
 						|| memcmp(buffer_test3, d, block_size) != 0
 					) {
-						fprintf(stderr, "Failed RAIDQP test\n");
+						fprintf(stderr, "Failed RAID test\n");
 						exit(EXIT_FAILURE);
 					}
 
@@ -491,12 +162,16 @@ static void raidQPtest(unsigned diskmax, unsigned block_size)
 	for(i=0;i<diskmax;++i) {
 		for(j=i+1;j<diskmax;++j) {
 			for(k=j+1;k<diskmax;++k) {
-				for(n=0;n<4;++n) {
+				for(n=0;n<sizeof(COMBO3)/sizeof(COMBO3[0]);++n) {
 					unsigned char* a;
 					unsigned char* b;
 					unsigned char* c;
 					unsigned char* p;
 
+					/* this is the point where quad parity fails over RAID_QUAD_DATA_LIMIT data disks */
+					if (diskmax > RAID_QUAD_DATA_LIMIT && COMBO3[n].use[2] >= 3)
+						continue;
+
 					/* save */
 					a = buffer[i];
 					b = buffer[j];
@@ -520,7 +195,7 @@ static void raidQPtest(unsigned diskmax, unsigned block_size)
 						|| memcmp(buffer_test1, b, block_size) != 0
 						|| memcmp(buffer_test2, c, block_size) != 0
 					) {
-						fprintf(stderr, "Failed RAIDQP test 1\n");
+						fprintf(stderr, "Failed RAID test\n");
 						exit(EXIT_FAILURE);
 					}
 
@@ -539,7 +214,7 @@ static void raidQPtest(unsigned diskmax, unsigned block_size)
 	/* check 2data */
 	for(i=0;i<diskmax;++i) {
 		for(j=i+1;j<diskmax;++j) {
-			for(n=0;n<6;++n) {
+			for(n=0;n<sizeof(COMBO2)/sizeof(COMBO2[0]);++n) {
 				unsigned char* a;
 				unsigned char* b;
 				unsigned char* p;
@@ -568,7 +243,7 @@ static void raidQPtest(unsigned diskmax, unsigned block_size)
 				if (memcmp(buffer_test0, a, block_size) != 0
 					|| memcmp(buffer_test1, b, block_size) != 0
 				) {
-					fprintf(stderr, "Failed RAIDQP test 1\n");
+					fprintf(stderr, "Failed RAID test\n");
 					exit(EXIT_FAILURE);
 				}
 
@@ -584,7 +259,7 @@ static void raidQPtest(unsigned diskmax, unsigned block_size)
 	}
 
 	/* check 1data */
-	for(n=0;n<4;++n) {
+	for(n=0;n<sizeof(COMBO1)/sizeof(COMBO1[0]);++n) {
 		for(i=0;i<diskmax;++i) {
 			unsigned char* a;
 			unsigned char* p;
@@ -613,7 +288,7 @@ static void raidQPtest(unsigned diskmax, unsigned block_size)
 
 			/* check */
 			if (memcmp(buffer_test0, a, block_size) != 0) {
-				fprintf(stderr, "Failed RAIDQP test\n");
+				fprintf(stderr, "Failed RAID test\n");
 				exit(EXIT_FAILURE);
 			}
 
@@ -746,9 +421,6 @@ void selftest(int gui)
 
 	hashtest();
 	crc32ctest();
-	raid5test(33, 1024);
-	raid6test(33, 1024);
-	raidTPtest(33, 1024);
-	raidQPtest(21, 1024);
+	raidtest(24, 2048);
 }