On 10/09/14 19:43, Goffredo Baroncelli wrote: > On 09/10/2014 02:27 PM, Bob Williams wrote: >> I have two 2TB disks formatted as a btrfs raid1 array, mirroring both >> data and metadata. Last night I started >> >> # btrfs filesystem balance <path> > > > May be that I am missing something obvious, however I have to ask which > would be the purpose to balance a two disks RAID1 system. > The balance command should move the data between the disks in order to > avoid some disk full and other empty; but this assume that there is a > not symmetrical uses of the disks. Which is not the case for a RAID1/two > disks system. > > If the disk were more than two the situation would be completely different. > But Bob reports that the system is compose by two disks only. > >> >> and it is still running 18 hours later. This suggests that most stuff >> only gets written to one physical device, which in turn suggests that >> there is a risk of lost data if one physical device fails. Or is >> there something clever about btrfs raid that I've missed? I've used >> linux software raid (mdraid) before, and it appeared to write to both >> devices simultaneously. >>
So if a RAID1/two disk system uses the disks symmetrically, why did my balance command take 22 hours? That's what puzzles me, as my understanding of RAID1 is that the disk use *is* symmetrical. Bob -- 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
