Re: [gentoo-user] Tips for fresh install with GRUB2+RAID1+LVM2

[Rich Freeman]

On Sun, May 17, 2015 at 6:08 PM, Stefan G. Weichinger <lists@×××××.at> wrote:
>
> There were problems with btrfs and the kernel a few months ago (Rich
> Freeman was hit by that, maybe he chimes in here), but in general for me
> it is still a very positive experience.
>

It is nowhere near the stability of ext4.  In the last year I've
probably had 2-3 periods of time where I was getting frequent panics,
or panics anytime I'd mount my filesystems rw.  That said, I've never
had an occasion where I couldn't mount the filesystem ro, and I've
never had an actual loss of committed data.  Just downtime while I
sorted things out.  I do keep a full daily rsnapshot backup on ext4
right now since I consider btrfs experimental.  However, if I were too
cheap to do that I wouldn't have actually lost anything yet.

On the other hand, both btrfs and zfs will get you a level of data
security that you simply won't get from ext4+lvm+mdadm - protection
from silent corruption.  The only time I've ever had a filesystem eat
my data on linux was on ext4+lvm+mdadm actually - when I googled for
the specific circumstances I think I ran into one guy on a list
somewhere who had the same problem, but it is pretty rare (and one
piece of advice I would give to anybody using lvm is to backup your
metadata - if I had done that and was more careful about running fsck
in repair mode I probably could have restored everything without
issue).  (For the curious, the issue was that I repaired a bunch of
fsck-detected problems in one filesystem and lost a lot of data in
another one.  I suspect that LVM got its mapping messed up somehow,
and it might have had to do with operating in degraded mode (perhaps
due to a crash and need for rebuild).)

A big advantage of btrfs/zfs is that everything is checksummed on
disk, and the filesystem is not going to rely on anything that isn't
internally consistent.  In the event of a rebuild/etc it can always
tell which copies are good/bad, unless you do something really crazy
like split an array onto two PCs, then rebuild both, and then try to
start mix the disks back together - from what I've heard btrfs lacks
generation numbers/etc needed to detect this kind of problem.

For personal use btrfs is great for playing around with the likely
future default linux filesystem.  I wouldn't go installing it on
production servers in a workplace unless it was a really niche
situation, and then only with appropriate steps to mitigate the risks
(lots of testing of new kernel releases, backups or an ability to
regenerate the system, etc).  I wouldn't go so far as to say that
there are no circumstances where it is the right tool for the job.
You should understand the pros/cons before using it, as with any tool.

-- 
Rich