Re: FreeBSD 5.3b7and poor ata performance

Quoting fandino <fandino_at_ng.fadesa.es>:

> Søren Schmidt wrote:
>>> # 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)
>>
>> etc, and I get this:
>> 1073741824 bytes transferred in 18.488903 secs (58074934 bytes/sec)
>> 1073741824 bytes transferred in 14.956484 secs (71791059 bytes/sec)
>
>>> 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.
>
> I redid all tests with __RC1__ and performance is as bad as before.
>
>> Now, raw performance is one thing, filesystem I/O something entirely
>
> I think the problem is with raw performace, just see this example
> with a test raid0. Each disk by separate has a throughput of 26000 K/sec,
> with /dev/stripe/test they have a throughput of 15000 K/sec each
> (raid0 throughput 30000 K/sec) and with four disks 7500 K/sec each
> (30000 K/sec again).
>
> # dd if=/dev/stripe/test of=/dev/null bs=1024k count=1024
> 1024+0 records in
> 1024+0 records out
> 1073741824 bytes transferred in 30.072215 secs (35705445 bytes/sec)
>
> There is a constant limit of 30000 K/sec independent of the number
> of disks used.
>
> simply it doesn't makes any sense. With two disk I'd must have
> approx. 26K+26K=52 M/sec and with four 26K+26K+26K+26K=104 M/sec
>
> Other systems like OpenBSD had a good throughput 55000K/sec by disk
>
> I send you in another email with all info that you need.
>
> Regards,
>
>
>
With this hardware:

atapci0: <Promise PDC20378 SATA150 controller> port 
0xdc00-0xdc7f,0xec00-0xec0f,
0xa000-0xa03f mem 0xfd800000-0xfd81ffff,0xfd900000-0xfd900fff irq 18 at 
device 8
.0 on pci0

ad4: 114440MB <Maxtor 6Y120M0/YAR51EW0> [232514/16/63] at ata2-master SATA150
ad6: 114440MB <Maxtor 6Y120M0/YAR51EW0> [232514/16/63] at ata3-master SATA150

Set up for striping:

ar0: 228880MB <ATA RAID0 array> [29178/255/63] status: READY subdisks:
  disk0 READY on ad4 at ata2-master
  disk1 READY on ad6 at ata3-master

I get the following performance with dd:

dd if=/dev/ad4 of=/dev/null bs=1m count=200
200+0 records in
200+0 records out
209715200 bytes transferred in 3.538456 secs (59267433 bytes/sec)

dd if=/dev/ad6 of=/dev/null bs=1m count=200
200+0 records in
200+0 records out
209715200 bytes transferred in 3.551439 secs (59050767 bytes/sec)

dd if=/dev/ar0 of=/dev/null bs=1m count=200
200+0 records in
200+0 records out
209715200 bytes transferred in 1.837508 secs (114130226 bytes/sec)

This is with a custom kernel with all debugging options off. I haven't seen a
mail from you yet that says whether you turned off debugging options in the
kernel or not, and if you haven't turned off debugging options, I'd strongly
suggest doing so.

Ken