On 2014-09-11 07:38, Hugo Mills wrote: > On Thu, Sep 11, 2014 at 07:19:00AM -0400, Austin S Hemmelgarn wrote: >> On 2014-09-11 02:40, Russell Coker wrote: >>> 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. > > Why change the default from 2-copies, which it's been for years?
Sorry about the ambiguity in my statement, I meant that the default for system chunks should be one copy per disk in the filesystem. If you don't have a copy of the system chunks, then you essentially don't have a filesystem, and that means that BTRFS RAID6 can't provide true resilience against 2 disks failing catastrophically unless there are at least 3 copies of the system chunks.
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