[CentOS] Re: Write performance with 3ware 9550

Bowie Bailey
Mon, 16 Oct 2006 20:43:20 -0000

Scott Silva wrote:
> Bowie Bailey spake the following on 10/12/2006 1:22 PM:
> > I have two identical servers.  The only difference is that the first
> > one has Maxtor 250G drives and the second one has Seagate 320G
> > drives.
> >
> > OS: CentOS-4.4 (fully patched)
> > CPU: dual Opteron 280
> > Memory: 16GB
> > Raid card: 3ware 9550Sx-8LP
> > Raid volume: 4-disk Raid 5 with NCQ and Write Cache enabled
> >
> > On the first server I have decent performance.  Nothing spectacular,
> > but good enough.  The second one has about 1/3 the write speed.  I
> > can't find any difference between the systems.  Both of them have
> > the same stripe size, both have ext3 filesystems, both have write
> > caching and NCQ turned on.  I have already increased the read ahead
> > setting to 16384 on both servers.
> >
> > I ran the tests like this:
> >
> > # sync; bonnie++ -d /iotest -s 50g -n 0 -b -f
> > (I have removed some extra information from the reports for brevity)
> >
> > And here are the results for the two servers:
> >
> >                     ------Output------- --Input--
> >                     --Block-- -Rewrite- --Block-- --Seeks--
> > Machine        Size K/sec %CP K/sec %CP K/sec %CP  /sec %CP
> > First           50G 62893  25 46763  12 160672  19 120.6   1
> > Second          50G 18835   7 44025  12 194719  24 122.8   1
> >
> > As you can see, the write performance of the second server is
> > terrible.  Anyone have any suggestions of what I can look for?  I
> > keep thinking there must be something I tweaked on the first server
> > that I forgot about for the second one, but so far I haven't been
> > able to find it.
> >
> > Any suggestions appreciated!
> >
> Is there a difference in the write performance, speed, or cache size
> of the drives?
> You didn't list specifics of the drives, so I had to ask.

There may be minor differences, but I would not expect this much
difference.

Actually, further testing has shown that the write performance on the
second machine varies anywhere from 20MB/Sec to 54MB/Sec depending on
when I test it.  Unfortunately, it appears random from my point of
view.  I'm still running tests to try to find a cause or at least a
related symptom.

The First system has Maxtor 7V250F0 drives (250GB).  The second system has
Seagate ST3500641AS drives (320GB).  They are both 7200RPM SATA II
drives with 16MB cache and NCQ support.

--
Bowie