[stgt] Using tgtd to pass through a SCSI tape drive

[Mark Harvey]

FUJITA Tomonori wrote:
> On Fri, 30 Jul 2010 16:55:51 +1000
> Mark Harvey <markh794 at gmail.com> wrote:
>
>   
>> So far, with this patch in place, it has passed all the current
>> NetBackup 'Drive Qualification tests'.
>> I'm just waiting on the last one to complete which writes random data
>> to complete tape to test EOT behaviour.
>>
>> As I've only got one spare tape in this library, I'm not sure if this
>> test will succeed as it is suppose to load a 2nd blank tape.. Oh well.
>> I'll check back in on progress once I'm at home to see if it
>> completed, otherwise it will be tomorrow.
>>
>> However, all tests so far have passed.
>>  - basic opening, closing & writing to tape
>>  - fast block locate tests
>>  - Force errors and check correct response
>>  - various reads/writes & positioning to check drive performance.
>>     
>
> Nice, thanks for testings!
>   
Unfortunately, my NetBackup host is connected via 100Mbit so is getting 
about 7.5Mbytes/sec (about 25-30G/Hr).
An Ultrium-4 drive writing to LTO3 tape is about 800G capacity. Hence 
the 'fill tape' test is still running.

> Probably, tgtd shouldn't set timeout. And tgtd also needs to pass
> through task management functions from initiators.
>
> The state of tgt pass though support is that it probably works, but it
> might useful on some cases.
>   
I'm not really up on 'task management' so I'm not really in a position 
to comment.

What I was thinking would be a "good idea"(tm) is for the bs_sg to issue 
a SCSI persistent reservation (exclusive) to the device under control, 
allow tgt to handle SCSI persistent reservation per initiator. This 
would prevent an application on the local host accessing the target 
while under tgt control.

Not sure if this falls under 'task management' or not.
It was just a thought. Not sure if it's worth the effort or not.
 
>> i.e.
>> Add a tested-by: Mark Harvey on this patch :)
>>
>> p.s.
>> As you have gone to the trouble to send a SCSI Inquiry to the device,
>> any chance of using that info to update "Type" message as well ?
>>     
>
> I merged a patch from Alexander so "passthough" type is
> printed. However, it might be better to print something like
> "tape (passthough)".
>
>   
Had similar thoughts myself.
Even if this is updated sometime after the 'sg_open()'. The window of 
opportunity where a user runs a '--op show' before the 'sg_open()' is 
called will be very short anyway.



Cheers
Mark

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