Re: All scsi_debug devices in the scsi_debug driver share the same RAM space

[Laurence Oberman <loberman@redhat.com>]

On Sat, 2018-02-03 at 14:43 -0500, Laurence Oberman wrote:
> Hello Doug
> 
> I had emailed you earlier about this issue forgetting to copy others.
> 
> All test devices in the scsi_debug driver share the same ram space so
> we cannot really have individual devices for testing stuff like md-
> raid.
> 
> I bumped into this a few times already and I think it would be useful
> to make each device an individual RAM entry so we can create multiple
> unique devices.
> 
> Of course this means also now having to maybe start using attributes
> for each device do we can selectively choose which devices get the
> fault injections.
> 
> I know its adding complexity here but wanted to get input about the
> possibility of changing this.
> 
> For a particular fault injection case this morning I had to use 5
> regular drives and 1 scsi-debug drive to inject faults to reproduce
> an
> md-raid issue.
> 
> I also wanted a different start sector and range and sent an earlier
> patch for that.
> 
> So is this something worth considering ?
> If so, i will start working on it.
> 
> Regards
> Laurence
> 
> 
> 
> 

I chatted with Doug about this.

Seems that many of the use cases for scsi_debug involved creating high
count devices for testing etc. so having each with its own ram space
could land up chewing a bunch of memory.

I am going to drop this idea for now, but the patch I sent for the
choice of sector for MEDIUM errors and count is very useful so I hope
that one gets accepted.
That patch changes nothing if the two new parameters are not set so
should be low risk for acceptance.

Thanks
Laurence