[stgt] make initiators "rescan" the device?

[Tomasz Chmielewski]

FUJITA Tomonori schrieb:
> On Wed, 29 Oct 2008 12:26:58 +0100
> Tomasz Chmielewski <mangoo at wpkg.org> wrote:
> 
>> Sometimes, I need to resize the device on the target.
>>
>> Technically, I do this as follows:
>>
>> lvextend -L+5G /dev/san14/blah1
>> tgt-admin --update tid=20 -v -f
> 
> What does exactly 'tgt-admin --update tid=20 -v -f' do? Please explain
> what tgtadm operations are performed. Please do so at all times (hint:
> I don't understand how tgt-admin works).

Basically, it disconnects all initiators, removes the target, and adds 
it again. Removing the lun and adding it again would be enough, as you 
also write below.


> Well, unless you delete a logical unit and add it again, tgtd doesn't
> know the new size. So probably, we need to a new interface to notify
> tgtd of the change.
> 
> 
>> However, the initiators won't see the change unless we "rescan" the 
>> device, i.e.:
>>
>> echo 1 > /sys/block/sdah/device/rescan
> 
> Unless you use 2.6.28-rc kernel, it doesn't work, I think.

It works for me with 2.6.18 kernels.


>> This is a boring thing to do when we have more initiators connected to 
>> that target.
>> Also, the initiators will likely have a different device used for that 
>> target (/sys/block/<DEVICE>/device/rescan), making the thing even more 
>> boring.
>>
>>
>> Is it possible to send a reset/rescan to all initiators connected to a 
>> given target, which would trigger the initiator to rescan the device 
>> (and its size)?
> 
> A scsi device can notify initiators of such event via UA (unit
> attention), google "CAPACITY DATA HAS CHANGED". tgt has the mechanism
> to handle UA so it's easy to support it. However, on the initiator
> side, Linux doesn't detect such event automatically.

I see.
So let's just hope Linux will detect such events one day ;)


-- 
Tomasz Chmielewski
http://wpkg.org
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