Phillip Susi wrote: > On 12/19/2012 11:45 AM, Jim Meyering wrote: >> Phillip Susi wrote: >>> Sure, take a 4 disk raid5 with 256k stripe factor. >> >> Am I misunderstanding something? 256k is both smaller than 1MiB and >> *is* a power of 2. I was asking if you'd seen values *not* like >> that. > > A 4 disk raid 5 with 256k stripe factor uses 256k from each of 3 disks > ( 4th is parity ), giving a stripe width and thus an optimal alignment > of 768k.
Ok, that makes sense. Then what do you think about lowering the bar from 1MiB to 128KiB? Maybe even 64KiB, I suppose. Better safe than sorry. Just look at how many people are still reporting problems with parted 1.8, so many years later. >> I guess it comes down to whether there are systems that return >> bogus values there, and whether there are systems that return legit >> values smaller < 1MiB, like I was asking about above. > > I'm not aware of any known bugs where the kernel returns inappropriate > values, but there are plenty of raid configurations that do use < 1MiB > and/or non power of two alignments. I'm pretty sure those tests do actually serve some purpose. Maybe Brian (Cc'd) knows for sure? (Brian, this is about the use of PED_DEFAULT_ALIGNMENT, aka 1MiB in commit c749046a54d983f74f8156c0aea71b0995b9477d)
