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On Sat, Mar 17, 2012 at 02:46:00PM +0100, Helmut Hullen wrote:
> Hallo, Hugo,
>
> Du meintest am 17.03.12:
>
> [no space left on device ...]
>
> >>> Where is the problem, how can I use the full space?
>
> >> Effectively it's missing the trigger to rebalance when the 'primary'
> >> device starts to get full, or just to randomly spread the data
> >> between the devices.
>
> > No, a balance isn't going to help here. RAID-0 requires a minimum
> > of 2 chunks in a block group. With two disks, you're only going to be
> > able to fill the smallest one before you run out of space.
>
> Ok - it happens only with 2 disks/Partitions?
Not quite. With the current RAID-0 implementation, you will lose
the difference between the largest disk and the second-largest.
There's a proposal from November that may help with that, but I
haven't had a chance to look at it yet to see what the implications
are.
> I've continued playing; added a 3rd partition/device and then balanced:
>
>
> # btrfs device add /dev/sdd1 /mnt/btr
> ## 73 + 146 + 146 GByte
OK, so in this case the largest and second-largest devices are the
same, so you will lose no space.
[snip]
> Looks as desired, the 3-disks-system contains more than 3 times the
> smallest disk.
>
> Balancing hasn't redistributed the contents - no problem.
>
> By the way: you should name the prefixes in the NIST way for powers of
> 2: KiB, MiB, GiB. Or change to decimal prefixes.
I know. It's something I submitted patches for a long time ago, and
they never got taken up. It's on my list of things to fix.
Hugo.
--
=== Hugo Mills: hugo@... carfax.org.uk | darksatanic.net | lug.org.uk ===
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