Re: FreeBSD 5.3b7and poor ata performance

fandino wrote:
> Hello Søren,
> 
> I was running FreeBSD-4.x for two years with this problem, waiting
> for FreeBSD-5 because ATAng looks very promising.
> 
> Unfortunately the performance problem persist :-( and I'd like to
> call the attention about performance over raw devices, whilst it's
> a very scientific test it's very curious:
> 
> # dd if=/dev/ad4 of=/dev/null bs=1024k count=1024
> 1024+0 records in
> 1024+0 records out
> 1073741824 bytes transferred in 31.090536 secs (34535970 bytes/sec)
> 
> over 34000 K/sec, using raw devices (for sequential access obviously)
> not softupdates, filesystems or caches are involved, and with all this
> FreeBSD performace is very deficient. Tests with OpenBSD and Linux
> using raw devices shows a throughput of approx 60000 K/sec.
> The question here is why using low-level access to disks is so bad?

I need more info on your system, ie config file dmesg etc.
 From what you've posted so far I've setup a system with a semilar disk 
etc, and I get this:

dd if=/dev/ad10 of=/dev/null bs=1024k count=1024
1024+0 records in
1024+0 records out
1073741824 bytes transferred in 18.488903 secs (58074934 bytes/sec)

On a WDC 70G raptor you will see:
# dd if=/dev/ad4 of=/dev/null bs=1024k count=1024
1024+0 records in
1024+0 records out
1073741824 bytes transferred in 14.956484 secs (71791059 bytes/sec)

So there is nothing in FreeBSD-5.3 thats hindering performance in the 
ATA subsystem as far as I can measure.

> Perphas I'm missing something but this seems very weird to me.

Most likely, as the result I get are close to what the disks can deliver.

> I'd like to know wich is you opinion about this.

If you run a stock generic kernel with the debug (WITNESS etc) taken out 
you should see the same raw performance as I do.

Now, raw performance is one thing, filesystem I/O something entirely 
different and not within my area of expertise. I do know that much 
though, that its very difficult to measure in a way that makes 
comparison between the different systems possible or even fair.

-- 

-Søren