[ewg] Re: cannot install SCST with SRP support

[Vu Pham]

Doron Shoham wrote:
> Vu Pham wrote:
>> In order to run with *scst_disk* you need to patch and rebuild the
>> kernel. Please follow SCST readme to do this task
>>
>> If you don't want to patch and rebuild the kernel, you can run with
>> *scst_vdisk* and get the same performance. I attach here an example to
>> setup *scst_vdisk*
>>
>>    -vu
> 
> Can you please explain me what is the differences between scst_disk and scst_vdisk?


scst_disk: scsi pass through module driver, using scsi 
mid-level interfaces to send commands

scst_vdisk: simulating file and block devices as scsi luns. 
Using file system interfaces (fileIO) and block interfaces 
(blockio) to send commands


> Is there any way to config SCST to work with RAM device (instead of working with a real
> scsi device)?

Yes. There are two ways

1. NULLIO or memory IO
a. dd if=/dev/zero of=/tmp/tempfile bs=64k count=100
b. echo "open vdisk0 /tmp/tempfile NULLIO" > 
/proc/scsi_tgt/vdisk/vdisk
c. echo "add vdisk0 0" > /proc/scsi_tgt/groups/Default/devices

2. Using ramdisk
a. echo "open vdisk1 /dev/ram0 BLOCKIO" > 
/proc/scsi_tgt/vdisk/vdisk
b. echo "add vdisk1 1" > proc/scsi_tgt/groups/Default/devices

Lun 0 with NULLIO will perform better