[gentoo-server] UUIDs in software RAID arrays

[gentoo-server] UUIDs in software RAID arrays

[A. Khattri]

raid1: raid set md2 active with 2 out of 2 mirrors
md: considering sdb3 ...
md:  adding sdb3 ...
md: sdb1 has different UUID to sdb3
md:  adding sda3 ...
md: sda1 has different UUID to sdb3
md: created md1


Does it really matter if the UUIDs are the same or not?



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Re: [gentoo-server] UUIDs in software RAID arrays

[Christoph Gysin]

A. Khattri wrote:
> raid1: raid set md2 active with 2 out of 2 mirrors
> md: considering sdb3 ...
> md:  adding sdb3 ...
> md: sdb1 has different UUID to sdb3
> md:  adding sda3 ...
> md: sda1 has different UUID to sdb3
> md: created md1
> 
> 
> Does it really matter if the UUIDs are the same or not?

Yes it does. Two devices with the same UUID build up one virtual md device.

What your seeing here is the noisy md module looking for matching devices. It compares every 
partition of type fd (linux autodetect) to any other with the same type.

On a system with lots of md devices, this looks like this:

md: Autodetecting RAID arrays.
md: autorun ...
md: considering hdc11 ...
md:  adding hdc11 ...
md: hdc10 has different UUID to hdc11
md: hdc9 has different UUID to hdc11
md: hdc8 has different UUID to hdc11
md: hdc7 has different UUID to hdc11
md: hdc6 has different UUID to hdc11
md: hdc5 has different UUID to hdc11
md: hdc3 has different UUID to hdc11
md: hdc1 has different UUID to hdc11
md:  adding hda11 ...
md: hda10 has different UUID to hdc11
md: hda9 has different UUID to hdc11
md: hda8 has different UUID to hdc11
md: hda7 has different UUID to hdc11
md: hda6 has different UUID to hdc11
md: hda5 has different UUID to hdc11
md: hda3 has different UUID to hdc11
md: hda1 has different UUID to hdc11
md: created md8
md: bind<hda11>
md: bind<hdc11>
md: running: <hdc11><hda11>
raid1: raid set md8 active with 2 out of 2 mirrors
md: considering hdc10 ...
md:  adding hdc10 ...
md: hdc9 has different UUID to hdc10
md: hdc8 has different UUID to hdc10
md: hdc7 has different UUID to hdc10
md: hdc6 has different UUID to hdc10
md: hdc5 has different UUID to hdc10
md: hdc3 has different UUID to hdc10
md: hdc1 has different UUID to hdc10
md:  adding hda10 ...
md: hda9 has different UUID to hdc10
md: hda8 has different UUID to hdc10
md: hda7 has different UUID to hdc10
md: hda6 has different UUID to hdc10
md: hda5 has different UUID to hdc10
md: hda3 has different UUID to hdc10
md: hda1 has different UUID to hdc10
md: created md7
md: bind<hda10>
md: bind<hdc10>
md: running: <hdc10><hda10>
raid1: raid set md7 active with 2 out of 2 mirrors
md: considering hdc9 ...
md:  adding hdc9 ...
md: hdc8 has different UUID to hdc9
md: hdc7 has different UUID to hdc9
md: hdc6 has different UUID to hdc9
md: hdc5 has different UUID to hdc9
md: hdc3 has different UUID to hdc9
md: hdc1 has different UUID to hdc9
md:  adding hda9 ...
md: hda8 has different UUID to hdc9
md: hda7 has different UUID to hdc9
md: hda6 has different UUID to hdc9
md: hda5 has different UUID to hdc9
md: hda3 has different UUID to hdc9
md: hda1 has different UUID to hdc9
md: created md6
md: bind<hda9>
md: bind<hdc9>
md: running: <hdc9><hda9>
raid1: raid set md6 active with 2 out of 2 mirrors
md: considering hdc8 ...
md:  adding hdc8 ...
md: hdc7 has different UUID to hdc8
md: hdc6 has different UUID to hdc8
md: hdc5 has different UUID to hdc8
md: hdc3 has different UUID to hdc8
md: hdc1 has different UUID to hdc8
md:  adding hda8 ...
md: hda7 has different UUID to hdc8
md: hda6 has different UUID to hdc8
md: hda5 has different UUID to hdc8
md: hda3 has different UUID to hdc8
md: hda1 has different UUID to hdc8
md: created md5
md: bind<hda8>
md: bind<hdc8>
md: running: <hdc8><hda8>
raid1: raid set md5 active with 2 out of 2 mirrors
md: considering hdc7 ...
md:  adding hdc7 ...
md: hdc6 has different UUID to hdc7
md: hdc5 has different UUID to hdc7
md: hdc3 has different UUID to hdc7
md: hdc1 has different UUID to hdc7
md:  adding hda7 ...
md: hda6 has different UUID to hdc7
md: hda5 has different UUID to hdc7
md: hda3 has different UUID to hdc7
md: hda1 has different UUID to hdc7
md: created md4
md: bind<hda7>
md: bind<hdc7>
md: running: <hdc7><hda7>
raid1: raid set md4 active with 2 out of 2 mirrors
md: considering hdc6 ...
md:  adding hdc6 ...
md: hdc5 has different UUID to hdc6
md: hdc3 has different UUID to hdc6
md: hdc1 has different UUID to hdc6
md:  adding hda6 ...
md: hda5 has different UUID to hdc6
md: hda3 has different UUID to hdc6
md: hda1 has different UUID to hdc6
md: created md3
md: bind<hda6>
md: bind<hdc6>
md: running: <hdc6><hda6>
raid1: raid set md3 active with 2 out of 2 mirrors
md: considering hdc5 ...
md:  adding hdc5 ...
md: hdc3 has different UUID to hdc5
md: hdc1 has different UUID to hdc5
md:  adding hda5 ...
md: hda3 has different UUID to hdc5
md: hda1 has different UUID to hdc5
md: created md2
md: bind<hda5>
md: bind<hdc5>
md: running: <hdc5><hda5>
raid1: raid set md2 active with 2 out of 2 mirrors
md: considering hdc3 ...
md:  adding hdc3 ...
md: hdc1 has different UUID to hdc3
md:  adding hda3 ...
md: hda1 has different UUID to hdc3
md: created md1
md: bind<hda3>
md: bind<hdc3>
md: running: <hdc3><hda3>
raid1: raid set md1 active with 2 out of 2 mirrors
md: considering hdc1 ...
md:  adding hdc1 ...
md:  adding hda1 ...
md: created md0
md: bind<hda1>
md: bind<hdc1>
md: running: <hdc1><hda1>
raid1: raid set md0 active with 2 out of 2 mirrors
md: ... autorun DONE.

Christoph
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Re: [gentoo-server] UUIDs in software RAID arrays

[A. Khattri]

On Thu, 13 Oct 2005, Christoph Gysin wrote:

> Yes it does. Two devices with the same UUID build up one virtual md device.

I thought so but this begs the question: is there any way of making md
less verbose?


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Re: [gentoo-server] UUIDs in software RAID arrays

[Kerin Millar]

On 10/13/05, A. Khattri <ajai@bway.net> wrote:
> On Thu, 13 Oct 2005, Christoph Gysin wrote:
>
> > Yes it does. Two devices with the same UUID build up one virtual md device.
>
> I thought so but this begs the question: is there any way of making md
> less verbose?
>

Not that I am aware of. However you could simply boot the kernel with
the "quiet" option and review the noise with the `dmesg` command or by
perusing your system log as and when the need arises.

Another approach would be to not use autodetection at all (see
/usr/src/linux/Documentation/md.txt) or to modify the md source code
directly.

Regards,

--Kerin Millar

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Re: [gentoo-server] UUIDs in software RAID arrays

[Christoph Gysin]

[-- Attachment #1: Type: text/plain, Size: 250 bytes --]

A. Khattri wrote:
> I thought so but this begs the question: is there any way of making md
> less verbose?

I patched md.c to be somewhat less verbose. Patch attached.

Christoph
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[-- Attachment #2: md-quiet.patch --]
[-- Type: text/plain, Size: 1662 bytes --]

--- drivers/md/md.c	2005-03-02 08:37:52.000000000 +0100
+++ drivers/md/md.c.quiet	2005-04-20 19:53:24.000000000 +0200
@@ -538,8 +538,10 @@
 		__u64 ev1, ev2;
 		mdp_super_t *refsb = (mdp_super_t*)page_address(refdev->sb_page);
 		if (!uuid_equal(refsb, sb)) {
+/*
 			printk(KERN_WARNING "md: %s has different UUID to %s\n",
 				b, bdevname(refdev->bdev,b2));
+*/
 			goto abort;
 		}
 		if (!sb_equal(refsb, sb)) {
@@ -1035,7 +1037,9 @@
 			
 	list_add(&rdev->same_set, &mddev->disks);
 	rdev->mddev = mddev;
+/*	
 	printk(KERN_INFO "md: bind<%s>\n", bdevname(rdev->bdev,b));
+*/
 	return 0;
 }
 
@@ -1767,8 +1771,10 @@
 		MD_BUG();
 		return;
 	}
-
+	
+/*
 	printk(KERN_INFO "md: running: ");
+*/
 
 	ITERATE_RDEV(mddev,rdev,tmp) {
 		char b[BDEVNAME_SIZE];
@@ -1803,18 +1809,24 @@
 	mddev_t *mddev;
 	char b[BDEVNAME_SIZE];
 
+/*	
 	printk(KERN_INFO "md: autorun ...\n");
+*/
 	while (!list_empty(&pending_raid_disks)) {
 		dev_t dev;
 		rdev0 = list_entry(pending_raid_disks.next,
 					 mdk_rdev_t, same_set);
 
+/*
 		printk(KERN_INFO "md: considering %s ...\n",
 			bdevname(rdev0->bdev,b));
+*/
 		INIT_LIST_HEAD(&candidates);
 		ITERATE_RDEV_PENDING(rdev,tmp)
 			if (super_90_load(rdev, rdev0, 0) >= 0) {
+/*			
 				printk(KERN_INFO "md:  adding %s ...\n",
 					bdevname(rdev->bdev,b));
+*/			
 				list_move(&rdev->same_set, &candidates);
 			}
@@ -1851,7 +1863,9 @@
 				mdname(mddev), bdevname(rdev0->bdev,b));
 			mddev_unlock(mddev);
 		} else {
+/*			
 			printk(KERN_INFO "md: created %s\n", mdname(mddev));
+*/			
 			ITERATE_RDEV_GENERIC(candidates,rdev,tmp) {
 				list_del_init(&rdev->same_set);
 				if (bind_rdev_to_array(rdev, mddev))