On Tue, Nov 4, 2014 at 9:15 PM, Anton Aylward
On 11/04/2014 06:53 PM, John Andersen wrote:
While installing 13.2 I let it use btrfs for root and xfs for /home partition.
Then you get these nebulous message that says some of the subvolumes of root are shadowed by other filesystems. That message means that you have a subvolume named /home defined in the /root automatically, and also a /home partition. Better language is needed for that error message. The term "Duplicate directory" names comes to mind. "Shadowed" is not very descriptive.
But then I began to wonder why btrfs defines subvolumes instead of letting the system define sub-directories?
Whats the difference in functionality? Are these sub-volume sizes fixed? Is it just part of the snapshot process? What's up with that?
I'm sure the designers had something in mind and its quite possibly documented somewhere. What follows is my thoughts and experience.
I did the installation as you described. Eventually the /home partition corrupted irretrievably. Its not a conventional reiserFS restored from a backup.
I'm glad I stayed with EXT4 for all partitions except /boot/efi with is FAT of course.
I think that the BtrFs model is that the FS should encompass the whole of the system as one logical volume possibly across many partitions or platters or spindles. It has that capability.
The subvolume mechanism, the manual says, can be treated like a directory or a moutned FS. Perhaps that's what is confusing about it. You can have a real (as in the XFS) mounted on /home or or ....
Well, in any other other FS if you don't mount the partition on /home you can still create stuff there, and when you do the actual mount it does overlay. "shadowed". So I asked myself why bother and cleared out all the subvolumes.
OUCH! That mean that /usr got DELETED. The subvolumes are not just markers. They really are directories.
Or are they? See https://lwn.net/Articles/579009/
*sigh* Re-install. "Learning experience".
This time I did without subvolumes and I can't say i missed them.
I'm sure that the idea behind BtrFS is that it can optimise the btree and space in some fantastic way. I'm sure that it really wants the whole of my 1T drive to be the BtrFS, including /boot and /swap. And I'm sure it can mirror onto another, and I'm sure that the subvolumes can be snapshotted and can then be used for a disk-to-disk-to-tape backup. I'm certain that just as my LVM partitions can grow and grow across spindles, so can BtrFS.
I am not, however, ready, to try installing a system on a single, encompassing single BtrFS. I'll let someone else try it and report. I'll also let someone else experiment with that BtrFS growing across many spindles.
https://btrfs.wiki.kernel.org/index.php/Main_Page
What I might experiment with, though, is this
<quote src="http://www.oracle.com/technetwork/articles/servers-storage-admin/advanced-btrfs-1734952.html"> Redundant Configuration
With Btrfs, you no longer need to use mdadm to create mirrored volumes or complex RAID configurations. These capabilities are built into the file system. </quote>
What I'm not clear on is how to extend an existing FS to become a BtrFS style RAIDFS.
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