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Linux and 4K disk sectors

Linux and 4K disk sectors

Posted Mar 12, 2009 1:55 UTC (Thu) by jimparis (subscriber, #38647)
Parent article: Linux and 4K disk sectors

The odd alignment trick only works if the partition tables are laid out that way -- for a while now, Windows has been starting the partition table at a 1MB boundary instead. H. Peter Anvin says "this is a disaster". Check out that whole thread from last month for more info.


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Linux and 4K disk sectors

Posted Mar 14, 2009 0:30 UTC (Sat) by giraffedata (subscriber, #1954) [Link]

And in big systems, disks often don't use DOS-partitioning, with some modern space manager taking the whole disk and allocating it at normal alignments. Most of the disks I use are that way. I guess those would fare poorly with odd alignment too.

Will the user get to choose between odd alignment and natural alignment? Or is the whole world going to be tuned for personal computers?

Linux and 4K disk sectors

Posted Mar 15, 2009 14:54 UTC (Sun) by willy (subscriber, #9762) [Link]

We're going to expose to userspace what the alignment is of this particular drive. Programs which lay out partitions (or partition-like things) will have to become aware of this problems. Filesystems should also care, so they don't cause the drive to do RMW.

Your average user-space program (be it 'cat' or openoffice) should let the filesystem do what it does best and ignore the underlying drive issues.

Linux and 4K disk sectors

Posted Mar 15, 2009 17:52 UTC (Sun) by giraffedata (subscriber, #1954) [Link]

Your average user-space program (be it 'cat' or openoffice) should let the filesystem do what it does best and ignore the underlying drive issues.

That's good, though the filesystem driver should also let the device driver do what it does best and ignore the underlying drive implementation. We learned a long time ago that there's value in having a generic block device interface, e.g. such that a filesystem driver doesn't concern itself with tracks and cylinders.

But I'm inferring from your silence that there will not be a way for the user to choose the alignment in the drive. That seems disastrous, since it means that at the very least everyone will need new device drivers to use the new drives with good performance (or maybe the RMW won't really be that noticeable?).

It would be a whole lot easier if the user could just get a special program to set the drive to the alignment his application requires and then use the drive with existing systems. I'd even say jumper-selectable, but I hear jumpers cost a fortune.


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