(S)ATA performance in FBSD 6.2/7.0
anderson at freebsd.org
Fri Mar 2 18:51:01 UTC 2007
On 03/02/07 09:28, Brooks Davis wrote:
> On Fri, Mar 02, 2007 at 10:38:35AM +0100, O. Hartmann wrote:
>> The last days I tried to figure out why some of my lab's FreeBSD boxes
>> and also mine at home seem to be outperformed by some Linux setups
>> around here and I saw something interesting.
>> On my lab's FreeBSD 6.2/i386 box (ASUS P4P800, ICH5 with two SATA 150
>> ports, two SATA 300 drives attached) I copied big files (~ 5GB) from one
>> drive to another while the box didn't do anything else than copying. I
>> watched the copy process via 'systat -vmstat 1' and realized, that the
>> value of 'KB/t' never go byond 128 (128kb buffer limit?). But more
>> frustrating, I never got beyond 33 MB/s transfer rate although
>> bonni/bonni++ told me both drives are capable doing much more (~75 MB/s
>> At home, I use a FreeBSD 7.0-CURRENT box on an ASUS
>> A8N32-SLI/nForce4-SLI based box, amd64 (no 32Bit compatibility). Two
>> Hitachi T7K250 250 GB/SATA II drives build up a RAID 0 (nVidia
>> MediaShield), and additionally there is a SAMSUNG Spinpoitn SP2004C
>> attached to the controller. bonni results in 55 MB/s for the SP2004C
>> alone and gives ~ 65 - 70 MB/s for the Hitachis, each and roughly 115
>> MB/s for the RAID 0. But copying from the single drive to the RAID 0 or
>> from the RAID 0 to the single drive also reaches this oscure 33 MB/s
>> In the first place I thought the older i386 hardware has some
>> hard-limits, but we have several boxes of the exact same hardware around
>> here and a wide spread Linux and Windows utilization and on those boxes
>> equipted with more than one harddrive (PATA or SATA) the effective
>> transfer rate shown up is about 50 - 65 MB/s as expected with copying a
>> big 5G file from one drive to another.
>> The hardwrae limit is completely nonsense when it comes to the AMD64 box
>> with newer hardware.
>> Before digging into this problem deeper with benchmarks, could anyone
>> explain why FreeBSD reaches this 33 MB/s limit (sounds like UDMA 33
>> defaults, but on both boxes nForce4 and ICH5 controller are recognized
>> and show up with SATA300 or SATA150 capabilities, respective)? May I
>> have some knobs I'm not aware of to tune disk performance?
>> I would appreciate any coments on that and if someone has some good
>> ideas how to benchmark those subjects, please let me know.
> One thing to keep in mind is that it matters a lot were on the disk you
> place the data due to the higher angular density of data at the outside
> of the disk. The results you are seeing are close to consistant with
> the kind of results I'd expect to see from writing at opposiste edges
> of the disk. The 33MB/s is suspious ane may diserve investigation, but
> make sure you are writing to the same part of the disk if you want to
> compare disk IO rates.
> There's an example of IO rates on recent large SATA disks:
> Also, you should time the actual copy and do the math to verify that
> vmstat is actually producing valid results. It's possible there's a bug
> in vmstat or the underlying statistics it uses.
I usually use gstat instead, but it might also be off (although my tests
in the past have not proven that).
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