Limiting disk data transfer rate, Any help greatly appreciated

Limiting disk data transfer rate, Any help greatly appreciated

[Vijay Kumar]

Hi All,

In my project we have a RAID connected to more than one machine via fibre 
channel switch. The RAID bandwidth is shared among  machines, some of them 
reading data at a high rate (for video streaming) and at lease one machine 
writing data into it. Since the raid bandwidth is limited, we would like to 
specify how the bandwidth is distributed among machines. This can not be 
done either in the FC switch or in the RAID, so my only option right now is 
have to specify the available bandwidth and limit the rate at which linux 
reads data from the RAID.

I am wondering if there is a way in the linux to specify the maximum 
bandwidth that could used with a disk. In other words I am looking for a 
driver level implementation that does the throttling when the maximum 
bandwidth limit is hit while reading/writing data to/from a disk.

Any help or pointers to possible solutions is greatly appreciated. I am not 
on the list, so please CC me with your responses and suggestions.


Thank you all

- Vijay

Re: Limiting disk data transfer rate, Any help greatly appreciated

[Richard B. Johnson]

On Mon, 6 May 2002, Vijay Kumar wrote:

> Hi All,
> 
> In my project we have a RAID connected to more than one machine via fibre 
> channel switch. The RAID bandwidth is shared among  machines, some of them 
> reading data at a high rate (for video streaming) and at lease one machine 
> writing data into it. Since the raid bandwidth is limited, we would like to 
> specify how the bandwidth is distributed among machines. This can not be 
> done either in the FC switch or in the RAID, so my only option right now is 
> have to specify the available bandwidth and limit the rate at which linux 
> reads data from the RAID.
> 
> I am wondering if there is a way in the linux to specify the maximum 
> bandwidth that could used with a disk. In other words I am looking for a 
> driver level implementation that does the throttling when the maximum 
> bandwidth limit is hit while reading/writing data to/from a disk.
> 
> Any help or pointers to possible solutions is greatly appreciated. I am not 
> on the list, so please CC me with your responses and suggestions.
> 
> 
> Thank you all
> 
> - Vijay

I think you can modify an existing driver, perhaps add an ioctl(), that
specifies the jiffy-count that the driver must sleep before doing each
I/O. Unfortunately, the granularity is rather large. One HZ might be
way to slow, and 0 HZ may be too fast. You can certainly experiment.

With some easy-to-write code, you can relate the sleep-interval to
the I/O length so you actually limit bandwidth.

If the system "almost" works, then you can modify HZ to get finer
granularity, perhaps 1024 would be a good value.

Cheers,
Dick Johnson

Penguin : Linux version 2.4.18 on an i686 machine (797.90 BogoMips).

                 Windows-2000/Professional isn't.