Re: Mixed and raid [was Re: BUG: btrfsRe: Does btrfs "raid1" actually provide any resilience?]

[Duncan <1i5t5.duncan@cox.net>]

Goffredo Baroncelli posted on Thu, 14 Nov 2013 22:21:22 +0100 as
excerpted:

> after some tests and looking at the code I discovered that the current
> mkfs.btrfs doesn't allow any raid profile other than SINGLE for data and
> meta-data when the mixed metadata/data group is enabled.

That'd be a big problem for me, here, as I run a separate sub-GiB (640 
MiB) btrfs filesystem /var/log, in data+metadata raid1 mode.  (The 
mountpoint is actually /lg, with /var/log a symlink pointing at it.)

btrfs f sh /lg

Label: lg0238gcnx+35l0  uuid: c77a9eb8-9841-4c2b-925e-75d0a925dcc3
        Total devices 2 FS bytes used 51.93MiB
        devid    1 size 640.00MiB used 288.00MiB path /dev/sdc4
        devid    2 size 640.00MiB used 288.00MiB path /dev/sda4

btrfs f df /lg

System, RAID1: total=32.00MiB, used=4.00KiB
Data+Metadata, RAID1: total=256.00MiB, used=51.92MiB

I've had a couple bad shutdowns, but btrfs scrub has reliably cleaned up 
the resulting mess on /lg due to open logfiles, and I'd be rather unhappy 
if that weren't possible.

Meanwhile, I also have two separate sub-GiB (256 MiB) /boot filesystems, 
one on each (of two) SSDs, with the grub2 on each pointing at its own 
/boot so a broken grub2 update won't break my ability to boot.

Those are both data+metadata dup mode:

btrfs f df /bt

System, DUP: total=8.00MiB, used=4.00KiB
System, single: total=4.00MiB, used=0.00
Data+Metadata, DUP: total=114.00MiB, used=41.38MiB
Data+Metadata, single: total=8.00MiB, used=0.00

You're saying data+metadata DUP wouldn't be possible here either, which 
would make me pretty unhappy too.

Fortunately I did those mkfs.btrfs on an earlier btrfs-tools so wasn't 
affected by this bug, but bug I would indeed call it, for sure!

-- 
Duncan - List replies preferred.   No HTML msgs.
"Every nonfree program has a lord, a master --
and if you use the program, he is your master."  Richard Stallman