Re: btrfs: mixing raid0 and raid1 - How?
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:
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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
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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
>
>
>
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