Re: Problem with iSCSI connected LTO-2 tape drive

[Lee Duncan]

> On Dec 28, 2016, at 4:48 AM, David C. Partridge 
>  wrote:
> 
> FWIW I still think the best solution is to suspend the NOP-Out polling (of 
> active) while a device command is being processed.  This way you get the best 
> of both worlds
>  
> However I do see the attraction of a documentation only fix J

LOL. It’s not (just) that I’m lazy. I honestly don’t think the code should 
change for this issue.

IMHO the NOP usage is a bad idea anyway, but it can be handy to detect a bad 
connection when no I/O is occurring.

The problem I think in this case is that open-iscsi does not treat tape and 
disc drives separately.

So if I send a command to a disc drive and don’t hear back for 8 minutes, I 
know that is not good. And for a disc drive, they always handle commands 
disconnected, i.e. the response for a read or write comes later, not when I 
request it. In that case, the disc brains does actually respond to PINGs while 
an operation is going on.

If we tried to add code that said “if any commands are outstanding don’t send 
PINGs”, then we could not catch the case where the disc server has gone away 
while a command was outstanding.

So unless you can come up with an idea that addresses this tape issue and 
regular usage, I don’t see any way to easily fix this.

But I’m open to suggestions. :)

>  
> Cheers
> Dave
>  
> From: open-iscsi@googlegroups.com  
> [mailto:open-iscsi@googlegroups.com ] On 
> Behalf Of The Lee-Man
> Sent: 22 December 2016 16:51
> To: open-iscsi
> Subject: Re: Problem with iSCSI connected LTO-2 tape drive
>  
> Hi David:
> 
> I have created Issue#35 for this on github.
> 
> On Thursday, December 15, 2016 at 2:00:15 PM UTC-8, David C. Partridge wrote:
> You’re right, it is in section 8.2.  Maybe it needs to be said in 8.1.1 as 
> well?
>  
> Dave
>  

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RE: Problem with iSCSI connected LTO-2 tape drive

[David C. Partridge]

FWIW I still think the best solution is to suspend the NOP-Out polling (of 
active) while a device command is being processed.  This way you get the best 
of both worlds

 

However I do see the attraction of a documentation only fix J

 

Cheers

Dave

 

From: open-iscsi@googlegroups.com [mailto:open-iscsi@googlegroups.com] On 
Behalf Of The Lee-Man
Sent: 22 December 2016 16:51
To: open-iscsi
Subject: Re: Problem with iSCSI connected LTO-2 tape drive

 

Hi David:

I have created Issue#35 for this on github.

On Thursday, December 15, 2016 at 2:00:15 PM UTC-8, David C. Partridge wrote:

You’re right, it is in section 8.2.  Maybe it needs to be said in 8.1.1 as well?

 

Dave

 

From: open-iscsi@googlegroups.com [mailto:open-iscsi@googlegroups.com] On 
Behalf Of Lee Duncan
Sent: 15 December 2016 19:41
To: open-iscsi@googlegroups.com
Subject: Re: Problem with iSCSI connected LTO-2 tape drive

 

On Dec 15, 2016, at 7:14 AM, david.partri...@perdrix.co.uk wrote:

 

Lee,

It would appear that the guilty party was:

node.conn[0].timeo.noop_out_interval = 5
node.conn[0].timeo.noop_out_timeout = 5

I changed both of these to 0 for the tape device and the problem went away.

 

Excellent.

 


Please note that the README.gz for open-scsi doesn't actually say that this is 
what you need to do to disable the NOP-out polling, so could I suggest that 
this be stated explicitly. 

 

My README says, in section 8.2:

 

For this setup, you can turn off iSCSI pings by setting:

 

node.conn[0].timeo.noop_out_interval = 0

node.conn[0].timeo.noop_out_timeout = 0

 

 

I must admit that I find it hard to imagine that an iSCSI target would reply to 
a NOP-out while it was processing a command such as a tape fsf or even tape 
erase (whose timeout is 6 * the long-timeout of 4 hours).  Should perhaps the 
NOP-out polling be suspended while a command is being processed?  Or 
alternatively maybe the NOP-out polling be completely disabled by default with 
something in the README.gz file that explains WHEN you might want it and how to 
enable it.   It's certainly clear that (at least) the MS iSCSI initiator 
doesn't send NOP-out polls.

 

open-iscsi is normally used to deal with discs. When it’s used with tape it’s 
not unusual to find bugs or design errors that we did not know were present.

 

Perhaps a small blurb in the README about dealing with tape, suggesting turning 
NOOP/ping off. Please feel free to post a pull request on github or suggest a 
patch on this list.

 

 


Regards
Dave

 

 

-- 

Lee Duncan

 

"Choice means saying no to one thing so you can say yes to another." -- Dan 
Millman

 

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