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 > > >
