>>>>> "Dave" == Dave Chinner <david@xxxxxxxxxxxxx> writes: >> Ok, if we have mismanaged the alignment and aligned to logical, not >> physical, then I guess there would be an issue... but at that point >> we've already messed up (though not catastrophically I guess)... Dave> That's where I'm concerned - if alignment is screwed because the Dave> FS is 512B sector aligned (because something read the logical Dave> sector size), then using a 4k sector will result in torn writes Dave> because every 4k sector write is potentially made up of 2 4k write Dave> IOs, not 1. There's another inherent failure scenario with 512b logical / 4096b physical. If you write in 512-byte multiples and experience a medium error you can lose the sibling logical blocks within that physical block. You'll get an I/O error back but there are no means to communicate that you have also lost blocks that were not part of your write request. So if you use 512-byte entries in the journal and get a write error you should at the very minimum consider adjacent entries inside a 4KB window suspect. Dave> That's my concern - using the logical 512b sector size is -always- Dave> safe, but using the 4k physical block size is only safe if Dave> everything under the filesystem has detected and used the physical Dave> block size of the disk for alignment and sector sizes... You should always take alignment into account. And while Christoph is right that (thankfully) nobody ended up shipping drives with 1-alignment by default, most 512e drives have the alignment jumper and some people actually use it. -- Martin K. Petersen Oracle Linux Engineering _______________________________________________ xfs mailing list xfs@xxxxxxxxxxx http://oss.sgi.com/mailman/listinfo/xfs
