[CentOS] Re: Write performance with 3ware 9550
Bowie_Bailey at BUC.com
Mon Oct 16 20:43:20 UTC 2006
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
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
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.
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