And:
39# btrfs filesystem show
Label: none uuid: 35db7af4-a116-45fa-8611-97aeb5d4a8d3
Total devices 3 FS bytes used 640.00KiB
devid 1 size 698.64GiB used 2.02GiB path /dev/sdg
devid 2 size 465.76GiB used 1.01GiB path /dev/sdh
devid 3 size 232.88GiB used 1.01GiB path /dev/sdi
Am 16.04.2016 um 12:05 schrieb Matthias Bodenbinder:
> Hello Luis,
>
> I followed that link which confirms that a btrfs raid1 out of these three
> devices should give 750 GB of data capacity. But his is not what I get.
>
> This is what I have:
>
> Disk /dev/sdg: 698,7 GiB, 750156374016 bytes, 1465149168 sectors
> Disk /dev/sdh: 465,8 GiB, 500107862016 bytes, 976773168 sectors
> Disk /dev/sdi: 232,9 GiB, 250058268160 bytes, 488395055 sectors
>
> So it is actually not 750 GB but 700. Anyways...
>
> This is what I did:
>
> ###############################################################
> 35# mkfs.btrfs -f -d raid1 -m raid1 /dev/sdg /dev/sdh /dev/sdi
> Btrfs v3.17
> See http://btrfs.wiki.kernel.org for more information.
>
> Turning ON incompat feature 'extref': increased hardlink limit per file to
> 65536
> adding device /dev/sdh id 2
> adding device /dev/sdi id 3
> fs created label (null) on /dev/sdg
> nodesize 16384 leafsize 16384 sectorsize 4096 size 1.36TiB
>
> 36# mount /dev/sdg /mnt/test/
>
> 37# btrfs fi df /mnt/test/
> Data, RAID1: total=1.00GiB, used=512.00KiB
> Data, single: total=8.00MiB, used=0.00B
> System, RAID1: total=8.00MiB, used=16.00KiB
> System, single: total=4.00MiB, used=0.00B
> Metadata, RAID1: total=1.00GiB, used=112.00KiB
> Metadata, single: total=8.00MiB, used=0.00B
> GlobalReserve, single: total=16.00MiB, used=0.00B
>
> 38# df -h /mnt/test/
> Dateisystem Größe Benutzt Verf. Verw% Eingehängt auf
> /dev/sdg 699G 17M 466G 1% /mnt/test
>
> ###############################################################
>
> This leaves me with just 466 GB of free disc space.
> Something is wrong. Either what I am doing is wrong or the web page is wrong.
>
> Matthias
>
>
> Am 16.04.2016 um 10:20 schrieb Luis Felipe Tabera Alonso:
>> On sábado, 16 de abril de 2016 9:00:00 (CEST) Matthias Bodenbinder wrote:
>>> Hello,
>>>
>>> I have 3 hard drive with 750 GB, 500 GB and 250 GB. I want to use btrfs as
>>> filesystem. This will be my first test installation of btrfs.
>>>
>>> My target is to get redundancy as well as a 750 GB data capacity. So I was
>>> thinking to create a raid0 with the 500 and 250 GB drive. This would result
>>> in a raid0 with 750 GB capacity. I want to add this raid0 as a mirror in a
>>> raid1 with the other 750 GB drive.
>>>
>>> But how do I do that?
>>>
>>> Thanks
>>> Matthias
>>
>> Disclaimer: I have necer made anything further than a btrfs raid1 with two
>> equally sized devices.
>>
>>
>> If you create a raid1 with the three devices you will get 750GB with
>> redundancy. Current Btrfs raid1 means "data and metadata is copied twice in
>> different devices". And btrfs is smart enough to not copy the data in the
>> two
>> smaller disks. I am not sure if this web page is accurate http://
>> carfax.org.uk/btrfs-usage/ but you can take a look.
>>
>> You can also create a single virtual device from the 250 and 500 devices
>> using
>> mdadm or lvm and then create a btrfs raid1 out of the 750GB device and the
>> virtual device.
>>
>> With the "pure" btrfs setup, if you lose a single device you will be able to
>> mount the device as "degraded".
>>
>> With the mixed setting, you can lose a single device and read the data.
>> Moreover, you can lose the two small devices and still be able to mount the
>> volume.
>>
>> luis
>>
>>
>>
>
>
>
