Re: Bad ext4 sync performance on 16 TB GPT partition

[Eric Sandeen <sandeen@redhat.com>]

Karsten Weiss wrote:
> Hi Eric,
> 
> On Fri, 26 Feb 2010, Eric Sandeen wrote:
> 
>>> => 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.
> 
> I think so because, as I mentioned, the issue can be reproduced with the 
> RH test kernel 2.6.18-190.el5 x86_64 (http://people.redhat.com/jwilson/el5/),
> too.
> 
>> 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.
> 
> Sorry for the delay, here's the (good) 2.6.32 result:
> 
> # /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, 46.3369 seconds, 226 MB/s
> 0.00user 14.17system 0:59.53elapsed 23%CPU (0avgtext+0avgdata 6224maxresident)k
> 0inputs+0outputs (0major+1045minor)pagefaults 0swaps
> 
> To summarize:
> 
> Bad:  2.6.18-164.el5 (CentOS)
> Bad:  2.6.18-164.11.1el5 (CentOS)
> Bad:  2.6.18-190.el5 (RH)
> Good: 2.6.32
> Good: 2.6.33
> 

Thanks, I'll have to investigate that.  I guess something may have gotten lost
in translation in the 2.6.32->2.6.18 backport.....

-Eric