Linux mdadm superblock question.
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From: david on 13 Feb 2010 15:50 On Sat, 13 Feb 2010, Justin Piszcz wrote: > On Sat, 13 Feb 2010, H. Peter Anvin wrote: > >> On 02/11/2010 05:52 PM, Michael Evans wrote: >>> On Thu, Feb 11, 2010 at 3:00 PM, Justin Piszcz <jpiszcz(a)lucidpixels.com> >>> wrote: >>>> Hi, >>>> >>>> I may be converting a host to ext4 and was curious, is 0.90 still the >>>> only >>>> superblock version for mdadm/raid-1 that you can boot from without having >>>> to >>>> create an initrd/etc? >>>> >>>> Are there any benefits to using a superblock > 0.90 for a raid-1 boot >>>> volume >>>> < 2TB? >>>> >>>> Justin. >>>> -- >>>> To unsubscribe from this list: send the line "unsubscribe linux-raid" in >>>> the body of a message to majordomo(a)vger.kernel.org >>>> More majordomo info at http://vger.kernel.org/majordomo-info.html >>>> >>> >>> You need the superblock at the end of the partition: If you read the >>> manual that is clearly either version 0.90 OR 1.0 (NOT 1.1 and also >>> NOT 1.2; those use the same superblock layout but different >>> locations). >> >> 0.9 has the *serious* problem that it is hard to distinguish a whole-volume >> >> However, apparently mdadm recently switched to a 1.1 default. I >> strongly urge Neil to change that to either 1.0 and 1.2, as I have >> started to get complaints from users that they have made RAID volumes >> with newer mdadm which apparently default to 1.1, and then want to boot >> from them (without playing MBR games like Grub does.) I have to tell >> them that they have to regenerate their disks -- the superblock occupies >> the boot sector and there is nothing I can do about it. It's the same >> pathology XFS has. >> >> -hpa >> > > My original question was does the newer superblock do anything special or > offer new features *BESIDES* the quicker resync? the older superblocks have limits on the number of devices that can be part of the raid set. David Lang -- 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: Michael Evans on 13 Feb 2010 16:10 On Sat, Feb 13, 2010 at 12:49 PM, <david(a)lang.hm> wrote: > On Sat, 13 Feb 2010, Justin Piszcz wrote: > >> On Sat, 13 Feb 2010, H. Peter Anvin wrote: >> >>> On 02/11/2010 05:52 PM, Michael Evans wrote: >>>> >>>> On Thu, Feb 11, 2010 at 3:00 PM, Justin Piszcz <jpiszcz(a)lucidpixels.com> >>>> wrote: >>>>> >>>>> Hi, >>>>> >>>>> I may be converting a host to ext4 and was curious, is 0.90 still the >>>>> only >>>>> superblock version for mdadm/raid-1 that you can boot from without >>>>> having to >>>>> create an initrd/etc? >>>>> >>>>> Are there any benefits to using a superblock > 0.90 for a raid-1 boot >>>>> volume >>>>> < 2TB? >>>>> >>>>> Justin. >>>>> -- >>>>> To unsubscribe from this list: send the line "unsubscribe linux-raid" >>>>> in >>>>> the body of a message to majordomo(a)vger.kernel.org >>>>> More majordomo info at �http://vger.kernel.org/majordomo-info.html >>>>> >>>> >>>> You need the superblock at the end of the partition: �If you read the >>>> manual that is clearly either version 0.90 OR 1.0 (NOT 1.1 and also >>>> NOT 1.2; those use the same superblock layout but different >>>> locations). >>> >>> 0.9 has the *serious* problem that it is hard to distinguish a >>> whole-volume >>> >>> However, apparently mdadm recently switched to a 1.1 default. �I >>> strongly urge Neil to change that to either 1.0 and 1.2, as I have >>> started to get complaints from users that they have made RAID volumes >>> with newer mdadm which apparently default to 1.1, and then want to boot >>> from them (without playing MBR games like Grub does.) �I have to tell >>> them that they have to regenerate their disks -- the superblock occupies >>> the boot sector and there is nothing I can do about it. �It's the same >>> pathology XFS has. >>> >>> � � � �-hpa >>> >> >> My original question was does the newer superblock do anything special or >> offer new features *BESIDES* the quicker resync? > > the older superblocks have limits on the number of devices that can be part > of the raid set. > > David Lang > The 1.1 and 1.2 formats ALSO play more nicely with stacking partition contents. LVM, filesystems, and partition info all begin at the start of a block device; putting the md labels there too makes it obvious what order to unpack the structures in. -- 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: H. Peter Anvin on 13 Feb 2010 16:40 On 02/13/2010 12:07 PM, Justin Piszcz wrote: > > My original question was does the newer superblock do anything special > or offer new features *BESIDES* the quicker resync? > 0.90 has a very bad problem, which is that it is hard to distinguish between a RAID partition at the end of volume and a full RAID device. This is because 0.90 doesn't actually tell you the start of the device. Then, of course, there are a lot of limitations on size, number of devices, and so on in 0.90. -hpa -- H. Peter Anvin, Intel Open Source Technology Center I work for Intel. I don't speak on their behalf. -- 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: Volker Armin Hemmann on 13 Feb 2010 21:00 >0.90 has a very bad problem, which is that it is hard to distinguish >between a RAID partition at the end of volume and a full RAID device. >This is because 0.90 doesn't actually tell you the start of the device. > >Then, of course, there are a lot of limitations on size, number of >devices, and so on in 0.90. but it is the only format supporting autodetection. So - when will autodetection be introduced with 1.X? And if not, why not? All I found was 'autodetection might be troublesome' and nothing else. But dealing with initrds is troublesome too. Pure evil even. Gl�ck Auf, Volker -- 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: Michael Evans on 13 Feb 2010 23:10
On Sat, Feb 13, 2010 at 5:51 PM, Volker Armin Hemmann <volkerarmin(a)googlemail.com> wrote: >>0.90 has a very bad problem, which is that it is hard to distinguish >>between a RAID partition at the end of volume and a full RAID device. >>This is because 0.90 doesn't actually tell you the start of the device. >> >>Then, of course, there are a lot of limitations on size, number of >>devices, and so on in 0.90. > > but it is the only format supporting autodetection. > > So - when will autodetection be introduced with 1.X? And if not, why not? > > All I found was 'autodetection might be troublesome' and nothing else. > �But dealing with initrds is troublesome too. Pure evil even. > > Gl�ck Auf, > Volker > -- > To unsubscribe from this list: send the line "unsubscribe linux-raid" in > the body of a message to majordomo(a)vger.kernel.org > More majordomo info at �http://vger.kernel.org/majordomo-info.html > I remember hearing that 1.x had /no/ plans for kernel level auto-detection ever. That can be accomplished in early-userspace leaving the code in the kernel much less complex, and therefore far more reliable. In other words, 'auto-detection' for 1.x format devices is using an initrd/initramfs. -- 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/ |