Partition scheme and file systems in dual boot environment [Solved]

Question

This machine is a general purpose desktop computer used by a single user. The plan is to run Arch primarily and have Ubuntu for backup. I have some experience with Arch and various other linux distros and usually just use a single partition for / with a separate /home partition. On my primary machine, however, I've accumulated a few disks and am wondering how I could best make use of what I have. I may eventually add a 256gb SSD or replace the 80gb drive with it, but currently this is what I have:
8gb SSD
80gb SSD
80gb HDD
1.5tb HDD
18gb RAM
Previously I kept almost everything on the 80gb SSD, including the home directory with individual folders for large files (VM's, music, video) stored on the 1.5tb drive and symlinked into my home directory. This worked very well, except the my home directory still wanted to grow fairly large over time as things accumulate (one culprit was my bitcoin wallet). If I did this again, it would be Arch on the 80gb SSD (probably using BTRFS), Ubuntu on the 80gb HDD (probably EXT4 or BTRFS), and a few different partitions on the 1.5tb drive, mostly BTRFS, depending on what will be stored.
My other thought was to install both operating systems to the 80gb SSD for maximum speed while putting the home directories on the 80gb HDD or on separate partitions of the 1.5tb drive.
In either case I'll probably make a /scratch mounted as a tmpfs to make better use of RAM.
So questions:
How much does speed matter generally for a home partition?
Is BTRFS a good choice for this kind of system? More trouble than it's worth?
Would an LVM make sense in this case? I'd assume there would be performance issues if I tried mixing SSD's and HDD's in an LVM.
What should I use the small 8gb SSD for?
Sorry if I've mixed terminology some here, I'm still learning!
Last edited by spurious_access (2013-07-12 15:51:37)

Answer 1

1) For most user data, speed is not really of consequence.  But what can matter is the speed of all the configuration files located in your home folder.  They are small, so decreased seek times are going to have a positive effect here.  This is the same reasoning as to why you would want the system configuration files in /etc to be on the SSD (not to mention you'd have a hell of a time separating /etc).
2) Btrfs is f*cking awesome! 
3) LVM could make sense, but it depends on what you want specifically.  The only reason you might have a performance hit with LVM2 is if you tried to apply some kind of RAID to it.  That is, striping and mirroring in LVM2 terms.  Obviously, vastly different speeds are going to do limited by whatever is slowest.  But the nice thing about LVM2 is that you can tell lvcreate to ensure that your logical volume is to be created all on one disk.  But btrfs is actually designed to handle disks of different sizes and to some extent, different speeds.
4) If the 8GB SSD is fast, then maybe you could use it as a nice root filesystem.  I honestly don't think I have ever had my root get any larger than 5GB.  But then I don't run a full DE either, but I also don't keep my system as mega-slim as possible like Trilby.  It might make sense to LVM over the two SSDs and maybe have a separate volume group over the two HDDs.  Or have one btrfs filesystem spanning the two SSDs and one spanning the two HDDs. 
Ultimately, the needs of your personal usage style is going to dictate what the actual best configuration of your machine is going to be.  But this hodge-podge of disks is defintiely not a terrible thing, and can actually probably be used quite efficiently.  It is totally up to you.
As a side note (in regard to my "btrfs is f*cking awesome" comment above), I tried btrfs about a year ago.  It was nice, but it was not quite where I had hoped.  But after doing something stoopid on my machine, and having to redo part of my setup, I decided to just rsync my system to another disk, create a btrfs pool, then rsync it back.  I couldn't be happier with my decision.  It is truly amazing the rate at which btrfs is progressing.  New features, more stability, faster speeds, it is all coming along quite nicely.