Re: 1x 3ware controllers vs. 2x 3ware controllers

[Mark Watts <mrwatts@fast24.co.uk>]

> Mark Watts wrote:
> > With the performance issues I'm seeing with the 8506-4LP's I have, I
> > wouldn't recommend them to anyone currently...
> >
> > The thread on LKML from a few days ago about mke2fs -j and 8506-4LP says
> > it all, but basically and reasonable amount of I/O brings a Dual Opteron
> > system to its knees.
> > And by reasonable I mean copying ISO images from a usb2 drive to a raid 5
> > (4 x 250GB maxtor) or even just formatting a 600MB partition.
>
> I would be interested to see the output of 'vmstat 1' while your system is
> so slow.
>
> IMHO you shouldn't draw such conclusion ("reasonable amount of I/O brings a
> Dual Opteron system to its knees") from your particular case. The 3 HT
> links of the Opteron make this CPU particularly adapted to I/O operations.

Well its the only conclusion I *can* come to at this time.
When you move from a UP 1.8Ghz P4 with single EIDE disks to SMP Opteron with 4 
times the ram and a hardware raid card, you tend to assume that performance 
in all areas will go up.
When it doesn't, and you find yourself watching screen redraws while you 
format a 600GB partition (ext3) you do feel the need to blame something :)

I'm all ears for suggestions on what me be wrong or things I can try to 
improve performance.


>
> Personnaly, on a dual Opteron, I am able to read datas from 4 SATA disks at
> about 225 MB/s, with CPU time used at about 32%, awd with a system still
> reasonably responsive.

I'm seeing ~80MB/sec reading from the 3ware raid-5 according to hdparm and 
bonnie++
Write performance is around 25MB/sec according to bonnie++.

Mark.