fedora 16, ext4 corruption

[Bill Davidsen]

Ian Malone wrote:
> Hi,
>
> Is anyone else seeing problems with F16 ext4? I recently moved my
> install onto a new harddisc (which is reporting SMART is fine after
> running a full test) and did that by making a new ext4 fs (previously
> ext3) then rsyncing across. I'm now seeing occasional system 'freezes'
> (not hard freezes, but programs can fail to start or freeze. Yesterday
> the desktop completely stopped, but I was able to switch to a virtual
> console). dmesg reports errors to do with failing to write the journal
> and remounting read-only. On reboot an fsck is required, which finds
> some fixable problems. Obviously I'm wondering if it's the OS or the
> new disc. Was planning an F18 install soon which might help with one
> problem but not the other.
> Don't know if it's the 'ext4 data corruption bug' or if that's been
> fixed. http://www.phoronix.com/scan.php?page=news_item&px=MTIxNDQ
>
I have multiple TB running on fc16+ext4, and have not seen any problems of any 
kind with the filesystem. I do occasionally see a hang, this happens with rsync 
if you copy something large to a machine with significant memory, at the end 
rsync does a sync() I believe (if it was doing fsync() I think the pain would be 
spread) and the system is emptying the i/o buffers to disk. A typical single 
disk will write at 50-100MB/s and if you have 4GB or more of backed up data, it 
will get slow. There are disk tuning tips you can use to spread the pain, but it 
makes the copy of small files run slower in many cases.

If you have a lot of small files, your journal may be full of incomplete 
transactions. The solution is to make the journal larger, I don't know if 
modifying the journal after the fact will change that, or even if it's the 
problem. I have played with putting journal on a faster device, 10k rpm drive, 
SSD, or memory (yes, just for testing, I know it's unsafe). Faster journal makes 
things faster with many small files.

Lots of thoughts for you to check against your particular problems.

-- 
Bill Davidsen <davidsen at tmr.com>
   "We have more to fear from the bungling of the incompetent than from
the machinations of the wicked."  - from Slashdot