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

[Ji Haitao]

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 1.00.05 is a bit out-of-date.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.