On 05/07/2012 10:52 AM, Helmut Hullen wrote:
Hallo, Felix,
Du meintest am 07.05.12:
I'm just going back to ext4 - then one broken disk doesn't disturb
the contents of the other disks.
?! If you use raid0 one broken disk will always disturb the contents
of the other disks, that is what raid0 does, no matter what
filesystem you use.
Yes - I know. But btrfs promises that I can add bigger disks and delete
smaller disks "on the fly". For something like a video collection which
will grow on and on an interesting feature. And such a (big) collection
does need a "gradfather-father-son" backup, that's no critical data.
With a file system like ext2/3/4 I can work with several directories
which are mounted together, but (as said before) one broken disk doesn't
disturb the others.
How can you do that with ext2/3/4? If you mean create several different
filesystems and mount them separately then that's very different from
your current situation. What you did in this case is comparable to
creating a raid0 array out of your disks. I don't see how an ext
filesystem is going to work any better if one of the disks drops out
than with a btrfs filesystem. Using -d single isn't going to be of much
use in this case either because that's like spanning a lvm volume over
several disks and then putting ext over that, it's pretty
nondeterministic how much you'll actually save should a large chunk of
the filesystem suddenly disappear.
It sounds like what you're thinking of is creating several separate ext
filesystems and then just mounting them separately. There's nothing
inherently special about doing this with ext, you can can do the same
thing with btrfs and it would amount to about the same level of
protection (potentially more if you consider [meta]data checksums
important but potentially less if you feel that ext is more robust for
whatever reason).
If you want to survive losing a single disk without the (absolute) fear
of the whole filesystem breaking you have to have some sort of
redundancy either by separating filesystems or using some version of
raid other than raid0. I suppose the volume management of btrfs is sort
of confusing at the moment but when btrfs promises you can remove disks
"on the fly" it doesn't mean you can just unplug disks from a raid0
without telling btrfs to put that data elsewhere first.
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