Re: Bad write performance with libata-tj-stable-2.6.17.4-20060710, pcmcia based sata_sil24, PMP, and NCQ drive

[Derek Taubert <taubert@geeks.org>]

On Fri, Sep 01, 2006 at 10:32:12PM +0900, Tejun Heo wrote:
> ># dd if=/dev/zero of=/dev/sda1 bs=4M count=512
> >
> >avg-cpu:  %user   %nice    %sys %iowait   %idle
> >           0.90    0.00    1.30   97.80    0.00
> >
> >Device:            tps    kB_read/s    kB_wrtn/s    kB_read    kB_wrtn
> >sda              15.00         0.00      1920.00          0      19200
> 
> Hmm... this really is weird.  FYI, you're the first to report such 
> problem.  As Jeff said, turning off write-back caching can have adverse 
> effect on write performance, but, then again, you previously reported 
> that the command queue is full.  Please update us on the write-back stuff.

>From searching the list archive, I gather this is controlled by "hdparm
-W"?

root@linux-srv:~ # hdparm -W 1 /dev/sda1                      

/dev/sda1:
 setting drive write-caching to 1 (on)
root@linux-srv:~ # dd if=/dev/zero of=/dev/sda1 bs=1M count=100
100+0 records in
100+0 records out
104857600 bytes (105 MB) copied, 53.8702 seconds, 1.9 MB/s
root@linux-srv:~ # hdparm -W 0 /dev/sda1                       

/dev/sda1:
 setting drive write-caching to 0 (off)
root@linux-srv:~ # dd if=/dev/zero of=/dev/sda1 bs=1M count=100
100+0 records in
100+0 records out
104857600 bytes (105 MB) copied, 53.7884 seconds, 1.9 MB/s

I'm going to try narrowing the scope of the test next.  Will purchase
an eSATA<->SATA cable today and try bypassing the port multiplier.

If that works, I'll try using one drive at a time on the PMP.

Thanks,
Derek