Moving/merging a filesystem back into /

Paul Slootman paul+rsync at
Tue Dec 3 09:29:39 MST 2013

On Tue 03 Dec 2013, Kevin Korb wrote:
> Sure.  Simply put, you can just change ext[23] to ext4 in fstab and it
> will just work.  Faster even.

Just be very sure that you have ext4 support in your kernel, otherwise
you have a problem. ext4 should be listed in /proc/filesystems .
Of course, the root filesystem is mounted before /etc/fstab can be
read... :-)  ignoring initrd for now.

> > There is a lot of FUD about reiserfs.
> Reiserfs can take a hard crash without needing an fsck just like
> ext[34] can.  This is what journaling is for.  I am talking about when
> fsck -p aborts and says you need to run fsck manually.  In ext[34]
> this is a minor inconvenience and you can usually even run fsck with
> - -y to just say yes to any prompts.  With reiserfs if you ever have a
> problem at this level you are screwed.

Not necessarily, but with reiser it's documented that reiser expects
_no_ storage failure whatsoever, so some form of RAID with redundancy is
a must.  You _are_ screwed if you happen to have an image of a reiser
filesystem on your reiser filesystem, as the fsck will see the reiser
markers and merge that image into your real filesystem.

I've avoided reiser since Hans got jailed for murder (but that's another
topic :-)

> I have seen it happen.  It is rare that reiserfs needs an fsck but if
> it does the fsck is destructive.

I've seen a reiser fsck eat the filesystem about 5 in 100 times.
(I used to help administer a server farm with 200 servers, running on
reiser at the time.)

> but the same is not true on Gentoo.  I used to use XFS for my media
> storage (it is great on large files) but I had to give it up because
> it had a bunch of weird problems interacting with NFS.

I used XFS with NFS for my dreambox (DVB satellite receiver), storing
multi-GB recordings. Of course there was only one NFS client. That
worked great. It's especially good at large files. That said, ext4 has
become quite amazing and even if it does fall mostly over, chances of
extracting files from the broken fs are excellent.

btrfs is promising to be quite cool as well, I love the snapshot system.
However having had some bad experiences with corruption I'm hesitant to
use it for anything critical for now. That _was_ a number of years ago,
on a 8TB filesystem which got hammered pretty badly with daily backups
(each being snapshotted and deleted after some time), so not really
representative of normal usage.


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