Linux mdadm superblock question.
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From: Gabor Gombas on 14 Feb 2010 16:30 On Sun, Feb 14, 2010 at 09:47:16PM +0100, Asdo wrote: > 1.x autodetection worked great for me in initramfs. Basically you > only need /etc/mdadm/mdadm.conf copied to initramfs (via > update-initramfs), There is no autodetection with 1.1. Once you have mdadm.conf you have pretty hard rules about what to look for and how to assemble it - ie. there is not much left to "auto" detect. Real autodetection would mean there is _no_ such information available, and you figure out everything by just looking at the devices you find. > initramfs procedure. > Also consider 1.x allows to choose which arrays are autoassembled > (hostname written in the array name equal to hostname in the machine > or specified in mdadm.conf): this is more precise than 0.9 which > autoassembles all, I think. And also causes much more pain when you install machines on an internal network where it gets a random name (in fact all new machines get the same temporary name), then it is moved to its real location and reconfigured with its real name. And you wonder why your arrays aren't assembled any more... Gabor -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
From: Henrique de Moraes Holschuh on 14 Feb 2010 16:30 On Sun, 14 Feb 2010, Asdo wrote: > >In my experience, every time we moved critical codepaths to userspace, we > >ended up decreasing the *overall* system reliability. > I don't see it like this. > You have the same chance to screw up the system by making mistakes > in the files in /etc, in the networking config, the firewall, the > server applications... Those don't require a reboot test to verify, and are far easier to rollback. Also, they can (and SHOULD) be done on testbeds. While the kind of screwup where an initramfs decides to bite you hard, usually cannot (they tend to happen when things already went horribly wrong). > (note: I speak for Debian/Ubuntu, redhat's initramfs I think is more messy.) > 1.x autodetection worked great for me in initramfs. Basically you > only need /etc/mdadm/mdadm.conf copied to initramfs (via > update-initramfs), the rest is done by Debian/Ubuntu standard > initramfs procedure. Yeah, cute. What happens when the initrd is not updated for whatever reason? That is a new failure mode that doesn't exist with 0.9 and kernel autorun. It boils down to whether failure modes new to 1.x without autorun are more likely to happen than the failure modes that are specific to 0.9 with autorun. IME, the 0.9 ones are less likely to happen, and I have been through quite a few incidents involving boot problems. Experience told me that initrds are far more prone to operator errors than the kernel autorun. Debian's *stable* initramfs creators have not screwed up on me yet, but I am well aware that they could. > Also consider 1.x allows to choose which arrays are autoassembled > (hostname written in the array name equal to hostname in the machine > or specified in mdadm.conf): this is more precise than 0.9 which > autoassembles all, I think. That can be either a good or bad thing depending on the situation, so I would never use it to count for (or against) 1.x or 0.9. -- "One disk to rule them all, One disk to find them. One disk to bring them all and in the darkness grind them. In the Land of Redmond where the shadows lie." -- The Silicon Valley Tarot Henrique Holschuh -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
From: Henrique de Moraes Holschuh on 14 Feb 2010 16:40 On Sun, 14 Feb 2010, H. Peter Anvin wrote: > IMO it would make sense to support autoassemble for 1.0 superblocks, and > making them the default. The purpose would be to get everyone off 0.9. > However, *any* default is better than 1.1. Well, FWIW, I would happily use (and recommend) 1.0 with auto-assemble (after verifying all the emergency repair toolset in use where I work has been upgraded to support it) in distros where the bootloader has enough of a clue to not bork on md-1.0 devices. Which should be most of the current crop. -- "One disk to rule them all, One disk to find them. One disk to bring them all and in the darkness grind them. In the Land of Redmond where the shadows lie." -- The Silicon Valley Tarot Henrique Holschuh -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
From: Gabor Gombas on 14 Feb 2010 17:10 On Sun, Feb 14, 2010 at 06:53:38PM +0000, John Robinson wrote: > True, but afaik every distro uses an initrd/initramfs and bundles > tools making it easy to manage and customise them, so what's the > problem? Distro provided initramfs generators have a bad habit assuming you patch/build your kernel like the distro does. If you want to use a vanilla kernel with different things built in/built as modules/not built at all, then you can get nasty surprises, and debugging can be rather painful. My current view is if you use a distro kernel, then you should also use an initramfs (in fact you do not have a choice). But if you want to build your own kernel, then you should get rid of the initramfs. Gabor -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
From: Rudy Zijlstra on 14 Feb 2010 22:30
H. Peter Anvin wrote: > In Fedora 12, for example, Dracut tries to make the distinction between > whole RAID device and a partition device, and utterly fails -- often > resulting in data loss. > > i do not use Fedora/redhat and do not intent to ever try them again... still, the point is valid > With a pointer to the beginning this would have been a trivial thing to > detect. > > IMO it would make sense to support autoassemble for 1.0 superblocks, and > making them the default. The purpose would be to get everyone off 0.9. > However, *any* default is better than 1.1. > > -hpa > > As long is autodetect is supported in the kernel, i am willing to upgrade to 1.0 superblocks. BUT i need the autodetect in the kernel, as i refuse to use initrd for production servers. Cheers, Rudy -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/ |