> Mitchell wrote: > With RAID10, there's still only 1 other copy, but the entire "original" disk is mirrored to another one, right?
No, full disks are never mirrored in any configuration. Here's how I understand Btrfs' non-parity redundancy profiles: single: only a single instance of a file exists across the file system dup: two instances of a file exist across the file system, and they may reside on the same physical disk (4.5.1+ required to use dup profile on multi-disk file system) raid1: same as dup but the instances are guaranteed to be on different disks raid0: single but can be striped between multiple disks raid10: data is guaranteed to exist on two separate devices but if n>2 the data is load balanced between disks* Even though my explanation is imperfect, I hopes that illustrates that Btrfs RAID is different than traditional RAID. Btrfs provides the same physical redundancy as RAID, but the implementation mechanisms are quite a bit different. This has wonderful consequences for flexibility, and it's what allowed me to run a 5x2TB RAID10 array for nearly two years and essentially allow complete allocation. The downside is that since allocations aren't enforced from start (eg. MD requiring certain number of disks and identical sizes), it's possible to get weird allocations over time, but the resolution is simple: run a balance from time to time. > Christoph wrote: > Especially, when you have an odd number devices (or devices with different sizes), its not clear to me, personally, at all how far that redundancy actually goes respectively what btrfs actually does... could be that you have your 2 copies, but maybe on the same device then? RAID1 (and transitively RAID10) guarantees two copies on different disks, always. Only dup allows the copies to reside on the same disk. This is guaranteed is preserved, even when n=2k+1 and mixed-capacity disks. If disks run out of available chunks to satisfy the redundancy profile, the result is ENOSPC and requires the administrator to balance the file system before new allocations can succeed. The question essentially is asking if Btrfs will spontaneously degrade into "dup" if chunks cannot be allocated on some devices. That will never happen. On Fri, Jun 3, 2016 at 1:42 PM, Mitchell Fossen <msfos...@gmail.com> wrote: > Thanks for pointing that out, so if I'm thinking correctly, with RAID1 > it's just that there is a copy of the data somewhere on some other > drive. > > With RAID10, there's still only 1 other copy, but the entire "original" > disk is mirrored to another one, right? > > On Fri, 2016-06-03 at 20:13 +0200, Christoph Anton Mitterer wrote: >> On Fri, 2016-06-03 at 13:10 -0500, Mitchell Fossen wrote: >> > >> > Is there any caveats between RAID1 on all 6 vs RAID10? >> Just to be safe: RAID1 in btrfs means not what RAID1 means in any >> other >> terminology about RAID. >> >> The former has only two duplicates, the later means full mirroring of >> all devices. >> >> >> Cheers, >> Chris. > -- > To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in > the body of a message to majord...@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
