Re: Feature Req: "mkfs.btrfs -d dup" option on single device

[Imran Geriskovan <imran.geriskovan@gmail.com>]

On 12/12/13, Chris Mason <clm@fb.com> wrote:
> For me anyway, data=dup in mixed mode is definitely an accident ;)
> I personally think data dup is a false sense of security, but drives
> have gotten so huge that it may actually make sense in a few
> configurations.

Sure, it's not about any security regarding the device.

It's about the capability of recovering from any
bit-rot which can creep into your backups and can be
detected when you need the file after 20-30 generations
of backups which is too late. (Who keeps that much
incremental archive and reads backup logs of millions of
files, regularly?)

> Someone asks for it roughly once a year, so it probably isn't a horrible
> idea.
> -chris

Today, I've brought up an old 2 GB Seagate from the basement.
Literaly, it has been "Rusted". So it deserves the title of
"Spinning Rust" for real. I had no hope whether it would work,
but out of curiosity I plugged it into a USB-IDE box.

It spinned up and wow!; it showed up among the devices.
It had two swap and an ext2 partition. I remembered that it was
one of the disk used for linux installations more than
10 years ago. I mounted it . Most of the files dates back to 2001-07.

They are more than 12 years old and they seem to be intact
with just one inode size missmatch. (See fsck output below).

If there were BTRFS (and -d dup :) ) at the time, now I would
perform a scrub and report the outcome here. Hence,
'Digital Archeology' can surely benefit from Btrfs. :)

PS: And regarding the "SSD data retension debate" this can be an
interesting benchmark for a device whick was kept in an unfavorable
environment.

Regards,
Imran


FSCK output:

fsck from util-linux 2.20.1
e2fsck 1.42.8 (20-Jun-2013)
/dev/sdb3 has gone 4209 days without being checked, check forced.
Pass 1: Checking inodes, blocks, and sizes
Special (device/socket/fifo) inode 82669 has non-zero size.  Fix<y>? yes
Pass 2: Checking directory structure
Pass 3: Checking directory connectivity
Pass 4: Checking reference counts
Pass 5: Checking group summary information

/dev/sdb3: ***** FILE SYSTEM WAS MODIFIED *****
/dev/sdb3: 41930/226688 files (1.0% non-contiguous), 200558/453096 blocks