Re: [PATCH v4 02/14] scsi_debug: add doublestore option

["Martin K. Petersen" <martin.petersen@oracle.com>]

Doug,

> The scsi_debug driver has always been restricted to using one (or
> none) ramdisk image for its storage. This means that thousands of
> scsi_debug devices can be created without exhausting the host
> machine's RAM. The downside is that all scsi_debug devices share the
> same ramdisk image. This option doubles the amount of ramdisk storage
> space with the first, third, fifth (etc) created scsi_debug devices
> using the first ramdisk image while the second, fourth, sixth (etc)
> created scsi_debug devices using the second ramdisk image.

I don't particularly like the idea that one has to know what first,
third, fifth, etc. are sharing backing storage and second, 24th, and
108th share a different backing.

I appreciate that % 2 is super simple. But I would much prefer to have
the backing store option be tied to a logical entity. Something like the
host, as we discussed a while back.

The default would be that all hosts share the same backing store like
they do now. And then add module parameter which allows each host to
have its own backing store. This allows greater flexibility in
configuring test setups and isn't substantially more complex than the
odd/even flip flop game, although it obviously means a bit of
fake_storep shuffling.

-- 
Martin K. Petersen	Oracle Linux Engineering