Re: [PATCH] relax checks to support 3disk raid6 arrays

[Andre Noll <maan@systemlinux.org>]

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On 11:09, Neil Brown wrote:

> Have you tried a 3-disk raid6 yet?  Any conclusions?

Yes, I played around a bit and used the two attached patches that
relax some checks in the kernel and in mdadm. It appears to work fine,
but I did only minimal testing with small loop devices, so I would
not recommend it for production use yet :)

Regards
Andre
-- 
The only person who always got his work done by Friday was Robinson Crusoe

[-- Attachment #1.2: 3disk-raid6-kernel.patch --]
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diff --git a/crypto/async_tx/async_pq.c b/crypto/async_tx/async_pq.c
index f375a27..2922e9f 100644
--- a/crypto/async_tx/async_pq.c
+++ b/crypto/async_tx/async_pq.c
@@ -395,7 +395,7 @@ async_pq_zero_sum(struct page **blocks, unsigned int offset, int src_cnt,
 	struct dma_async_tx_descriptor *tx = NULL;
 	enum dma_ctrl_flags dma_flags = cb_fn ? DMA_PREP_INTERRUPT : 0;
 
-	BUG_ON(src_cnt < 2);
+	BUG_ON(src_cnt < 1);
 
 	if (device && src_cnt <= dma_maxpq(device, 0) - 2) {
 		dma_addr_t dma_src[src_cnt + 2];
@@ -486,7 +486,7 @@ async_syndrome_zero_sum(struct page **blocks, unsigned int offset, int src_cnt,
 	struct dma_async_tx_descriptor *tx = NULL;
 	enum dma_ctrl_flags dma_flags = cb_fn ? DMA_PREP_INTERRUPT : 0;
 
-	BUG_ON(src_cnt < 2);
+	BUG_ON(src_cnt < 1);
 
 	if (device && src_cnt <= dma_maxpq(device, 0) - 2) {
 		dma_addr_t dma_src[src_cnt + 2];
diff --git a/crypto/async_tx/async_xor.c b/crypto/async_tx/async_xor.c
index 50cd370..70869bb 100644
--- a/crypto/async_tx/async_xor.c
+++ b/crypto/async_tx/async_xor.c
@@ -183,7 +183,7 @@ async_xor(struct page *dest, struct page **src_list, unsigned int offset,
 	struct dma_chan *chan = async_tx_find_channel(depend_tx, DMA_XOR,
 						      &dest, 1, src_list,
 						      src_cnt, len);
-	BUG_ON(src_cnt <= 1);
+	BUG_ON(src_cnt < 1);
 
 	if (chan) {
 		/* run the xor asynchronously */
diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index a76ef52..5ce7090 100644
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -4357,8 +4357,8 @@ static raid5_conf_t *setup_conf(mddev_t *mddev)
 		       mdname(mddev), mddev->new_layout);
 		return ERR_PTR(-EIO);
 	}
-	if (mddev->new_level == 6 && mddev->raid_disks < 4) {
-		printk(KERN_ERR "raid6: not enough configured devices for %s (%d, minimum 4)\n",
+	if (mddev->new_level == 6 && mddev->raid_disks < 3) {
+		printk(KERN_ERR "raid6: not enough configured devices for %s (%d, minimum 3)\n",
 		       mdname(mddev), mddev->raid_disks);
 		return ERR_PTR(-EINVAL);
 	}

[-- Attachment #1.3: 3disk-raid6-mdadm.patch --]
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diff --git a/Create.c b/Create.c
index 9e65d0a..bd79838 100644
--- a/Create.c
+++ b/Create.c
@@ -96,7 +96,7 @@ int Create(struct supertype *st, char *mddev, int mdfd,
 			Name ": a RAID level is needed to create an array.\n");
 		return 1;
 	}
-	if (raiddisks < 4 && level == 6) {
+	if (raiddisks < 3 && level == 6) {
 		fprintf(stderr,
 			Name ": at least 4 raid-devices needed for level 6\n");
 		return 1;

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