Problem with concurrent SATA-Writes

Problem with concurrent SATA-Writes

[Tobias Reinhard]

Hi All!

I have a problem with two SATA-Discs. I have an onboard SIL3114 with 
four SATA-Ports an onboard NVIDIA with two SATA-Ports - both controllers 
are disable via BIOS (and are not detected by Linux)(only for this test 
of course - normally I have other HDD on this ports). The only 
controller that is found is the add-on controller in a PCI-Slot 
(SIL3112). And that is the one I have trouble with.

If I read or write  (via dd) from the first one -> no problems. Same 
when read or write from the second or when I read (only read!) from both 
at the same time. Data-Transfer-Rate is around 45MB/s for one HDD.

The problem occures when I try to write on both discs at the same time. 
For example I write /dev/zero to the first one and then start to write 
/dev/zero to the second one. The System-Load goes up to 4 with nearly 
100% io-wait and nearly no really write-access to the drives.

Any hints?

- no errormessages in syslog
- happens with Kernel 2.6.11.7 and with 2.6.12-rc5
- HDDs are Samsung Spinpoint 200GB
- (I use the SCSI-SATA-Drivers)
- anything else you need?

Thanks

Tobias

Problem with concurrent SATA-Writes

[Tobias Reinhard]

I have a problem with two SATA-Discs. I have an onboard SIL3114 with
four SATA-Ports an onboard NVIDIA with two SATA-Ports - both controllers
are disable via BIOS (and are not detected by Linux)(only for this test
of course - normally I have other HDD on this ports). The only
controller that is found is the add-on controller in a PCI-Slot
(SIL3112). And that is the one I have trouble with.

If I read or write  (via dd) from the first one -> no problems. Same
when read or write from the second or when I read (only read!) from both
at the same time. Data-Transfer-Rate is around 45MB/s for one HDD.

The problem occures when I try to write on both discs at the same time.
For example I write /dev/zero to the first one and then start to write
/dev/zero to the second one. The System-Load goes up to 4 with nearly
100% io-wait and nearly no write-access to the drives.

Any hints?

- no errormessages in syslog
- happens with Kernel 2.6.11.7 and with 2.6.12-rc5
- HDDs are Samsung Spinpoint 200GB
- (I use the SCSI-SATA-Drivers)

Tobias

Re: Problem with concurrent SATA-Writes

[Lennart Sorensen]

On Tue, May 31, 2005 at 07:16:42PM +0200, Tobias Reinhard wrote:
> I have a problem with two SATA-Discs. I have an onboard SIL3114 with
> four SATA-Ports an onboard NVIDIA with two SATA-Ports - both controllers
> are disable via BIOS (and are not detected by Linux)(only for this test
> of course - normally I have other HDD on this ports). The only
> controller that is found is the add-on controller in a PCI-Slot
> (SIL3112). And that is the one I have trouble with.
> 
> If I read or write  (via dd) from the first one -> no problems. Same
> when read or write from the second or when I read (only read!) from both
> at the same time. Data-Transfer-Rate is around 45MB/s for one HDD.
> 
> The problem occures when I try to write on both discs at the same time.
> For example I write /dev/zero to the first one and then start to write
> /dev/zero to the second one. The System-Load goes up to 4 with nearly
> 100% io-wait and nearly no write-access to the drives.
> 
> Any hints?
> 
> - no errormessages in syslog
> - happens with Kernel 2.6.11.7 and with 2.6.12-rc5
> - HDDs are Samsung Spinpoint 200GB
> - (I use the SCSI-SATA-Drivers)

Might it be a problem with having two things using /dev/zero at the same
time?

What blocksize do you use with dd?

What happens if you do dd from /dev/zero to two different files on one
of the hds (with some filesystem on the drive obviously)?

How about:
dd if=/dev/zero bs=128k| tee >(dd of=/dev/disk1 bs=128k) | dd of=/dev/disk2 bs=128k

That seems pretty fast here (writing to two files in /tmp rather than
two disks since I don't have two disks I can just destroy.).

Len Sorensen

Re: Problem with concurrent SATA-Writes

[Tobias Reinhard]

Lennart Sorensen wrote:
 > Might it be a problem with having two things using /dev/zero at the same
 > time?
No, dding from /dev/zero two times at the same time is working perfectly

 > What blocksize do you use with dd?
Generally I use 1M. But the Problem is the same with 128k or with 4k

 > What happens if you do dd from /dev/zero to two different files on one
 > of the hds (with some filesystem on the drive obviously)?
I did it without a FS on it and its no problem to write at two different 
locations - as long as they are on one disc.

It seems to me that the driver has problems with handling two 
write-requests on two ports at the same time.

Tobias