Re: EXT4 is ~2X as slow as XFS (593MB/s vs 304MB/s) for writes?

[Eric Sandeen <sandeen@redhat.com>]

Justin Piszcz wrote:
> Hello,
> 
> Is it possible to 'optimize' ext4 so it is as fast as XFS for writes?
> I see about half the performance as XFS for sequential writes.
> 
> I have checked the doc and tried several options, a few of which are shown
> below (I have also tried the commit/journal_async/etc options but none
> of them get the write speeds anywhere near XFS)?
> 
> Sure 'dd' is not a real benchmark, etc, etc, but with 10Gbps between 2
> hosts I get 550MiB/s+ on reads from EXT4 but only 100-200MiB/s write.
> 
> When it was XFS I used to get 400-600MiB/s for writes for the same RAID
> volume.
> 
> How do I 'speed' up ext4?  Is it possible?
> 

FWIW I'm seeing similar things on fast storage (Fusion IO),
though this is under 2.6.31.  500MB/s+ for xfs, 300 for ext4.

Overwriting an existing file is no faster.   I don't think this
driver is blktraceable but I'll try a newer driver that should be I think.

(xfs's overwrite went from 534 to 597 mb/s; ext4 sat at 320-ish)

direct IO was good for both xfs & ext4 at around 530mb/s

I'll see if I can get this running on a more recent kernel to
do further investigation.

-Eric