Re: [dm-devel] Why it can not support more than 100 targets in 1 MD ?

[Ji Haitao <jiht ict ac cn>]

Kevin Corry wrote:
> On Thursday 01 April 2004 20:46, Ji Haitao wrote:
>
> > I create a MD having 100 targets with dmsetup. IO error occurs when I
> > access the 100th target. My operation steps are :
> >
> > 1.#create md
> > sh> dmsetup create vd1 dmtable1
> >
> > 2.
> > #access the 100th target
> > sh> dd bs=512 count=10 if=/dev/zero of=/dev/mapper/vd1 seek=51380224
> >
> > #errors happen
> > dd: writing `/dev/mapper/vd1': Input/output error
> > 1+0 records in
> > 0+0 records out
>
>
> I ran your 100-target table on one of my systems. Did a dd of the entire 
> device with no I/O errors. I'm running device-mapper.1.00.08 on a 2.6.5-rc3 
> kernel.
>
>
> > If I only have 99 targets in dmtable1, everything is OK when I access
> > the 99th target. Why? If device-mapper can support more than 100 targets
> > in 1 MD ?
>
>
> > The configuration of my Linux host is:
> > CPU: P4 1.4G
> > MEM: 512M
> > Kernel: 2.4.21
> > device-mapper.1.00.05
> > dd (fileutils) 4.1.9
>
>
> 1.00.05 is a bit out-of-date. I'd suggest upgrading to device-mapper.1.00.09 
> (upgrade both the tools and the kernel patches) and see if the problem 
> persists.

Thank Kevin Corry very much!

I upgraded my device-mapper from 1.00.05 to 1.00.09 and everything is OK 
now.

I did more tests and verified that device-mapper.1.00.09 can support 
more than 204,800 linear targets on a linux host with 128M RAM and work 
well. When I tried to add 2,048,000 targets, dmsetup told me the memory 
was not enough, but device-mapper did not crash. I think this is OK.