On Thu, 10 May 2012 19:42:10 +0200 Piergiorgio Sartor <piergiorgio.sartor@xxxxxxxx> wrote: > Hi, > > after the RAID-5 problem, I just realized that > other RAIDs I have, including a multi RAID-6, > have different data offset for each component. > > This seems to be quite of a problem, in case > "Create" is used to recover an array. > > Obviouly, if a 4 disks RAID-5 has 2 disks with > one offset and 2 with another, it will not be > possible to re-create it (saving the data). I certainly won't be easy. Though if someone did find themselves in that situation it might motivate me to enhance mdadm in some way to make it easily fixable. > > Is there any way to fix/prevent such issue? > Shouldn't "mdadm" make sure all offset are > the same? Or try, at least... I'm not sure. Maybe... With linux-3.5 and mdadm-3.3 (both unreleased) you will probably be able to mdadm --grow --data-offset=5M and that will happen. At least for RAID10. Other levels might follow later. Should mdadm keep them always the same? The reason that it doesn't is that I thought that you could change the data offset by removing each device and adding it back as a spare with a new data_offset. Maybe that isn't such a good idea. I suspect that I got a chorus of people all saying "please keep data_offset consistent" - and particular if I received a patch which did that - then I would probably change mdadm accordingly. NeilBrown > > What I noticed is that, adding a disk later, > might cause different offsets. > > Any idea? > > Thanks, > > bye, >
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