Hi,
Since I had some free time over Christmas, I decided to conduct few
tests over btrFS to se how it will cope with "real life storage" for
normal "gray users" and I've found that filesystem will always mess up
your files that are larger than 10GB.
Long story:
I've used my set of data that I've got nicelly backed up on personal
raid 5 to populate btrfs volumes: music, slr pics and video (an just a
few document). Disks used in test are all "green" 2TB disks from WD.
1. First I started with creating btrfs (4k blocks) on one disk, filling
it up and then adding second disk -> convert to raid1 through balance ->
convert to raid10 trough balance. Unfortunately converting to raid1
failed - because of CRC error in 49 files that vere bigger > 10GB. At
this point I was a bit spooked up that my controllers are failing or
that drives got some bad sectors. Tested everything (took few days) and
it turns out that there is no "apparent" issue with hardware (bad
sectors or io down to disks).
2. At this point I thought "cool this will be a perfect test case for
scrub to show it's magical power!". Created raid1 over two volumes ->
try scrubbing -> FAIL ... It turns out that magically I've got corrupted
CRC in two exactly same logical locations (~34 files > 10GB affected).
3. Performed same test on raid10 setup (still 4k block). Same results
(just diffrent file count).
Ok, time to dig more into this because it starts get intriguing. I'm
running ubuntu server 12.10 with stock kernel, so my next step was to
get 3.7.1 kernel + new btrfs tool straight from git repo.
Unfortunatelly 1 & 2 & 3 still provides same results, corrupt CRC only
in files > 10GB.
At this point I thought "fine maybe when I'll expand allocation block -
it will make less block needed for big file to fit in resulting in
propperly storing those" -> time for 16K leafs :) (-n 16K -l 16K)
sectors are still 4K for known reasons :P. Well, it does exactly the
same thing -> 1 & 2 & 3 same results, big files get automagically corrupt.
Something about test data:
music - not more than 200MB files (tipical mix of mp3 & aac) 10 K files
give or take.
pics - not more than 20MB (typical point & shot + dslr) 6K files give or
take.
video1 - collection of little ones with size more than 300MB, less than
1.5GB ~ 400 files
video2 - collection of 5GB - 18GB files ~400 files
I guess that stating that "files >10GB" are only affected is a long
shot, but so far I've not seen file less than 10GB affected (I was not
really thorough about checking size, but all files that size I've
checked were more than 10GB)
ps. As a footnote I'll add that I've tried shuffling test 1, 2 & 3
without video2 and it all work just fine.
If you've got any ideas for work around ( other than zfs :D ) I'm happy
to try it out.
Tom.
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