BTRFS dup profile woes...

The_Great_Sephiroth · Posted: Sun Oct 01, 2017 8:58 pm Post subject: BTRFS dup profile woes...

I've been experimenting with BTRFS on my laptop and I hit a stopping point. I want the DUP profile for my home subvolume/partition/whatever, but using DUP on the OS wastes loads of space. I normally do a BIOS or GPT partition, then a BTRFS partition, then an ext4 for VirtualBox systems, and finally a swap partition. I make BTRFS subvolumes for /boot, /usr/src, /, and /home. This allows me to use different compression methods on different locations. None for boot, LZO for the system root, and ZLIB for home and the kernel sources. The issue is that subvolumes cannot change data profiles, meaning either the entire system is DUP or SINGLE.

With this in mind, I am left with either no duplicate data for my important work documents, duplicate data for EVERYTHING, requiring me to purchase an even larger disk (1TB currently), or go back to multiple partitions, something like BTRFS A for the OS in single mode and BTRFS B for /home in DUP mode. What would you guys do? I am debating two BTRFS partitions instead of one. If so, how much space should I give it for the entire OS with KDE/Plasma, K3B, LibreOffice, KDEnlive, Code::Blocks, etc? Remember, if I go this route the OS partition will be in single mode.

So, what would you do?
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The_Great_Sephiroth · Posted: Tue Oct 03, 2017 4:06 pm Post subject:

OK, I have about decided to go to a BTRFS partition for the OS and one for /home. The OS will use the single profile and the home partition will use the DUP profile. However, how big of a partition should I use for the OS? Below are the packages I use.

pjp · Administrator Joined: 16 Apr 2002 Posts: 20067

Zucca · Posted: Tue Oct 03, 2017 8:28 pm Post subject:

Iirc I've asked about this feature (different profiles on subvolumes) in #btrfs and the answer was "It's in the works".
But as we all know - creating a current generation filesystem is a slow process. I've also asked if there was planned support to have user selectable number of copies btrfs makes from each file... At that time it was only "frequently asked feature".

So you might have the features you need eventually. Thus I'd create a setup that is easy to change to use single big btrfs when the time comes.
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The_Great_Sephiroth · Posted: Tue Oct 03, 2017 9:02 pm Post subject:

This would be simple to change in the future. Boot System Rescue CD, move /home to an external device (USB for example), delete the /home partition, extend the OS partition to fill the void, move /home back. Easy, but not a big concern since it is one of many features still being developed.

The OS is currently consuming zero bits of space since I zeroed the disk with dd before realizing I should have checked usage first. I am likely going to have /var/tmp/portage and /usr/portage on an external disk attached by eSATA to save space. Actually, maybe just the build directory. This way I can search portage on the go. Either way it will save some space.

I believe I am going to try 150GiB and if that works and leaves me 20~30GiB free, I am happy. I want a partition large enough to house the OS but to have 20-20% free. If it has more free, I can shrink the partition. I will post back when everything is done and report my install size.

Oh and by "loads" I mean half. DUP is simply RAID1 on a single disk. If I had a partition of 100GiB in DUP I'd only be able to fit 50GiB onto it since two copies of each chunk of data are stored. Great for redundancy when sectors fail or rot, but bad for storage!
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Ever picture systemd as what runs "The Borg"?