On 2014-09-11 02:40, Russell Coker wrote: > On Mon, 8 Sep 2014, Austin S Hemmelgarn <ahferro...@gmail.com> wrote: >> Also, I've found out the hard way that system chunks really should be >> RAID1, NOT RAID10, otherwise it's very likely that the filesystem >> won't mount at all if you lose 2 disks. > > Why would that be different? > > In a RAID-1 you expect system problems if 2 disks fail, why would RAID-10 be > different? That's still the case, but in a RAID1 with four disks, of the six different pairs of two disks you could lose, only one will make the filesystem un-mountable, whereas for a four disk RAID10, there are two different pairs of two disks you could lose to make the filesystem un-mountable. In haven't run the numbers for higher numbers of disks, but things are likely not better, because if you lose both copies of the same stripe, things will fail. > > Also it would be nice if there was a N-way mirror option for system data. As > such data is tiny (32MB on the 120G filesystem in my workstation) the space > used by having a copy on every disk in the array shouldn't matter. > N-way mirroring is in the queue for after RAID5/6 work; ideally, once it is ready, mkfs should default to one copy per disk in the filesystem.
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