Re: Bad ext4 sync performance on 16 TB GPT partition

[Eric Sandeen <sandeen@redhat.com>]

Karsten Weiss wrote:
> Hi Dmitry!
> 
> On Fri, 26 Feb 2010, Dmitry Monakhov wrote:
> 

...

>>> * I did not try a vanilla kernel so far.
>> IMHO It would be really good to know vanilla kernel's stats.
> 
> I did a quick&dirty compilation of vanilla kernel 2.6.33 and repeated the 
> test:
> 
> # /usr/bin/time bash -c "dd if=/dev/zero of=/mnt/large/10GB bs=1M count=10000 && sync"
> 10000+0 records in
> 10000+0 records out
> 10485760000 bytes (10 GB) copied, 50.044 seconds, 210 MB/s
> 0.01user 13.76system 1:04.75elapsed 21%CPU (0avgtext+0avgdata 6224maxresident)k
> 0inputs+0outputs (0major+1049minor)pagefaults 0swaps
> 
> => The problem shows only with the CentOS / Red Hat 5.4 kernels (including 
> RH's test kernel 2.6.18-190.el5). Aadmittedly ext4 is only a technology 
> preview in 5.4...
> 
> I've also tried the latest CentOS 5.3 kernel-2.6.18-128.7.1.el5 but 
> couldn't mount the device (with -t ext4dev).
> 
> 2.6.18-164.el5 (the initial CentOS 5.4 kernel) has the bug, too.
> 
> I'm willing to test patches if somebody wants to debug the problem.

Ok, that's interesting.  We've not had bona-fide RHEL customers report
the problem, but then maybe it hasn't been tested this way.

2.6.18-178.el5 and beyond is based on the 2.6.32 codebase for ext4.

Testing generic 2.6.32 might also be interesting as a datapoint,
if you're willing.

-Eric