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- May 17, 2014
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Something came up where I wanted to test booting off 2 different root volumes in Linux using it's LVM & EXT4. I figured I'd simply copy my existing root FS, (which uses ZFS), and modify the "/etc/fstab" for "/" as appropriate.
Well, I saw my ZFS root was about 10GB. So I created my 2 root volumes in LVM as 10GB. Then copied to one LVM volume with Rsync. But, it did not stop when it was the same size, it keep growing!
I then realized my root pool's top level dataset used LZ4 compression, and everything inherited that attribute. I had not realized that I had gotten that good of compression, (see below). In the back of my mind I know ZFS, (without compression), can take more space due to checksumming and metadata copies. But, net gain when using LZ4 compression? Great. Something else to love about ZFS.
Well, I saw my ZFS root was about 10GB. So I created my 2 root volumes in LVM as 10GB. Then copied to one LVM volume with Rsync. But, it did not stop when it was the same size, it keep growing!
root@laptop:/# df -h / /mnt/usb
Filesystem Size Used Avail Use% Mounted on
rpool/root/20180220 9.7G 3.7G 6.0G 39% /
/dev/mapper/rootdg-rootv1 9.8G 5.8G 3.6G 62% /mnt/usb
I then realized my root pool's top level dataset used LZ4 compression, and everything inherited that attribute. I had not realized that I had gotten that good of compression, (see below). In the back of my mind I know ZFS, (without compression), can take more space due to checksumming and metadata copies. But, net gain when using LZ4 compression? Great. Something else to love about ZFS.
root@laptop:/# zfs get all rpool/root/20180220 | grep comp
rpool/root/20180220 compressratio 1.77x -
rpool/root/20180220 compression lz4 inherited from rpool