On 2/20/20 9:08 PM, Douglas Gilbert wrote: > 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. > > The reason for doing this is to check that (partial) disk to disk > copies based on scsi_debug devices have actually worked properly. > As an example: assume /dev/sdb and /dev/sg1 are the same > scsi_debug device, while /dev/sdc and /dev/sg2 are also the > same scsi_debug device. With doublestore=1 they will have > different ramdisk images. Then the following pseudocode could > be executed to check the if sgh_dd copy worked: > dd if=/dev/urandom of=/dev/sdb > sgh_dd if=/dev/sg1 of=/dev/sg2 [plus option(s) to test] > cmp /dev/sdb /dev/sdc > > If the cmp fails then the copy has failed (or some other > mechanism wrote to /dev/sdb or /dev/sdc in the interim). > > Signed-off-by: Douglas Gilbert <dgilbert@xxxxxxxxxxxx> > --- > drivers/scsi/scsi_debug.c | 264 +++++++++++++++++++++++++++----------- > 1 file changed, 186 insertions(+), 78 deletions(-) > Nice use-case, but really should be documented somewhere. Otherwise: Reviewed-by: Hannes Reinecke <hare@xxxxxxx> Cheers, Hannes -- Dr. Hannes Reinecke Kernel Storage Architect hare@xxxxxxx +49 911 74053 688 SUSE Software Solutions Germany GmbH, Maxfeldstr. 5, 90409 Nürnberg HRB 36809 (AG Nürnberg), GF: Felix Imendörffer
