> > On Jun 16, 2015, at 8:25 AM, Hugo Mills <[email protected]> wrote: > > On Tue, Jun 16, 2015 at 08:09:17AM -0400, Vincent Olivier wrote: >> >> "btrfs filesystem df” gives : >> >> >> Data, RAID10: total=7.08TiB, used=7.02TiB >> Data, single: total=8.00MiB, used=0.00B >> System, RAID10: total=7.88MiB, used=656.00KiB >> System, single: total=4.00MiB, used=0.00B >> Metadata, RAID10: total=9.19GiB, used=7.56GiB >> Metadata, single: total=8.00MiB, used=0.00B >> GlobalReserve, single: total=512.00MiB, used=0.00B > >> My first question is this : is it normal to have “single” blocks ? >> Why not only RAID10? I don’t remember the exact mkfs options I used >> but I certainly didn’t ask for “single” so this is unexpected. > > Yes. It's an artefact of the way that mkfs works. If you run a > balance on those chunks, they'll go away. (btrfs balance start > -dusage=0 -musage=0 /mountpoint)
Thanks! I did and it did go away, except for the "GlobalReserve, single: total=512.00MiB, used=0.00B”. But I suppose this is a permanent fixture, right? > >> My second question is : what is the best device add / balance sequence to >> use if I want to add 2 more disks to this RAID10 volume? Also is a balance >> necessary at all since I’m adding a pair? > > Add both devices first, then balance. > > For a RAID-1 filesystem, adding two devices wouldn't need a balance > to get full usage out of the new devices. However, you've got RAID-10, > so the most you'd be able to get on the FS without a balance is four > times the remaining space on one of the existing disks. > > The chunk allocator for RAID-10 will allocate as many chunks as it > can in an even number across all the devices, omitting the device with > the smallest free space if there's an odd number of devices. It must > have space on at least four devices, so adding two devices means that > it'll have to have free space on at least two of the existing ones > (and will try to use all of them). > > So yes, unless you're adding four devices, a rebalance is required > here. It is perfectly clear and logical that 1+0 works on four devices at a time. >> My third question is: given that this file system is an offline >> backup for another RAID0 volume with SMB sharing, what is the best >> maintenance schedule as long as it is offline? For now, I only have >> a weekly cron scrub now, but I think that the priority is to have it >> balanced after a send-receive or rsync to optimize storage space >> availability (over performance). Is there a “light” balancing method >> recommended in this case? > > You don't need to balance after send/receive or rsync. If you find > that you have lots of data space allocated but not used (the first > line in btrfs fi df, above), *and* metadata close to usage (within, > say, 700 MiB), *and* no unallocated space (btrfs fi show), then it's > worth running a filtered balance with -dlimit=3 or some similar small > value to free up some space that the metadata can expand into. Other > than that, it's pretty much entirely pointless. Ok thanks. Is there a btrfs-utils way of automating the "if less than 1Gb free do balance -dlimit=3” ? > For maintenance, I would suggest running a scrub regularly, to > check for various forms of bitrot. Typical frequencies for a scrub > are once a week or once a month -- opinions vary (as do runtimes). Yes. I cronned it weekly for now. Takes about 5 hours. Is it automatically corrected on RAID10 since a copy of it exist within the filesystem ? What happens for RAID0 ? Thanks! V-- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
