ATA 4 KiB sector issues.
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From: Tejun Heo on 16 Mar 2010 22:10 Hello, On 03/17/2010 12:22 AM, Martin K. Petersen wrote: >>>>>> "Tejun" == Tejun Heo <tj(a)kernel.org> writes: > > Tejun> * Anything remotely modern (>= XP) doesn't give a hoot about > Tejun> cylinder alignment. > > Tejun> * Anything older (<= 2000) is very likely to get confused with > Tejun> custom geometry starting from the BIOS itself. For those > Tejun> cases, the only thing we can do is aligning partitions to > Tejun> cylinders abiding BIOS supplied geometry parameters which will > Tejun> usually be 255/63. > > Tejun> So, using custom geometry doesn't help compatibility at all. > > Great reads on this topic. Might be worth linking to: > > http://www.win.tue.nl/~aeb/partitions/partition_types.html > http://www.win.tue.nl/~aeb/linux/largedisk.html Thanks for the links. I'll read and link them. BTW, if you can spot something wrong regarding this in the doc, please let me know. I'm still learning how all these legacy stuff is supposed to work so there likely are some points that I got wrong. -- tejun -- 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: Kevin Easton on 16 Mar 2010 23:10 James Bottomley wrote: > On Wed, 2010-03-17 at 00:20 +0900, Tejun Heo wrote: .... > > Well, the thing is that > > > > * Anything remotely modern (>= XP) doesn't give a hoot about cylinder > > alignment. > > > > * Anything older (<= 2000) is very likely to get confused with custom > > geometry starting from the BIOS itself. For those cases, the only > > thing we can do is aligning partitions to cylinders abiding BIOS > > supplied geometry parameters which will usually be 255/63. > > > > So, using custom geometry doesn't help compatibility at all. > > Our partitioning tool still obey the integral cylinder rule ... we can > argue about whether they should, but what we need is a strategy for > fixing what is rather than what should be. James / Tejun, Can't we fix the problem by defaulting to aligning partitions to start on an LBA that is a multiple of 64260 ? Such partitions will always be 4KiB-aligned, *and* start-of-cylinder aligned (assuming 255/63, as seems to be the norm). Sure, that reduces your partition granularity to almost-32-MiB, but that's pretty small potatoes these days (and it's only a *default*, so you could always override that if you really cared, and didn't need the compatibility). - Kevin -- 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: Tejun Heo on 16 Mar 2010 23:50 Hello, On 03/17/2010 11:51 AM, Kevin Easton wrote: > Can't we fix the problem by defaulting to aligning partitions to > start on an LBA that is a multiple of 64260 ? > > Such partitions will always be 4KiB-aligned, *and* start-of-cylinder > aligned (assuming 255/63, as seems to be the norm). > > Sure, that reduces your partition granularity to almost-32-MiB, but > that's pretty small potatoes these days (and it's only a *default*, so > you could always override that if you really cared, and didn't need > the compatibility). The only thing we can gain by that is possible compatibility w/ very old operating systems (<=w2k, BTW, it would be great if someone can actually test it). Plus, breaking the first cylinder assumption might not be always safe to begin with. I personally don't think it's something worth departing from the behavior most vendors would assume from now on (1MiB alignment). It should be enough and safer to provide a mechanism to choose legacy alignment if someone is trying to put something which is older than a decade there. Thanks. -- tejun -- 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 17 Mar 2010 02:50 On 03/16/2010 06:24 AM, James Bottomley wrote: > > Because the msdos label can only partition in units of cylinders. If > you're using an msdos label, picking the right H/S gets you alignment. > This is doubly false. An MS-DOS partition table can partition at any boundary. Some OSes (like some versions of MS-DOS) needed track alignment because their boot loaders did not support crossing track boundaries. Second, the primary field in the (modern) MS-DOS partition table is an LBA field. The CHS fields are largely historic and useless because of the 1024-cylinder limitation, and by only being 24 bits total. -hpa -- 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: jdow on 17 Mar 2010 04:20
From: "Tejun Heo" <tj(a)kernel.org> Sent: Tuesday, 2010/March/16 20:44 > Hello, > > On 03/17/2010 11:51 AM, Kevin Easton wrote: >> Can't we fix the problem by defaulting to aligning partitions to >> start on an LBA that is a multiple of 64260 ? >> >> Such partitions will always be 4KiB-aligned, *and* start-of-cylinder >> aligned (assuming 255/63, as seems to be the norm). >> >> Sure, that reduces your partition granularity to almost-32-MiB, but >> that's pretty small potatoes these days (and it's only a *default*, so >> you could always override that if you really cared, and didn't need >> the compatibility). > > The only thing we can gain by that is possible compatibility w/ very > old operating systems (<=w2k, BTW, it would be great if someone can > actually test it). Plus, breaking the first cylinder assumption might > not be always safe to begin with. I personally don't think it's > something worth departing from the behavior most vendors would assume > from now on (1MiB alignment). It should be enough and safer to > provide a mechanism to choose legacy alignment if someone is trying to > put something which is older than a decade there. > > Thanks. > > -- > tejun WRT very old filesystems - it won't affect Amiga partition tables or the Amiga FFS. It already understands large block sizes natively. And that's MY definition of "old" with "very" in front of it. {^_^} Joanne Dow -- 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/ |