Re: Problem with file system on iSCSI FileIO

From: Slawomir Nowakowski <slawomir.nowakowski@open-e.com>
To: Emmanuel Florac <eflorac@intellique.com>,
	Christoph Hellwig <hch@infradead.org>
Cc: "Artur Piechocki" <artur.piechocki@open-e.com>,
	"Łukasz Wittig" <lukasz.wittig@open-e.com>,
	"'Ryszard Stawiarski'" <ryszard.stawiarski@open-e.com>,
	xfs@oss.sgi.com
Subject: Re: Problem with file system on iSCSI FileIO
Date: Fri, 24 Sep 2010 15:49:10 +0200	[thread overview]
Message-ID: <4C9CAC56.2020601@open-e.com> (raw)
In-Reply-To: <20100924151846.1208611c@harpe.intellique.com>

Dear Sirs,
> Le Fri, 24 Sep 2010 03:55:05 -0400
> Christoph Hellwig<hch@infradead.org>  écrivait:
>
>    
>> Thanks, I know ISCSI very well.  But what is "iSCSI FileIO" ?  The
>> above sounds like it's an iscsi target, is that correct?
>>      
> It's an IO Mode that goes through the kernel VFS cache, as opposed to
> blockIO that does direct IO.
>
>    
>> I still can't make any sense of the actual setups.
>>
>> The above seems to be the backend storage.  Then there's SCST
>> somewhere in which is in a out of tree kernel module.  And then you
>> use XFS somewhere.  Please provide a full description of the setup.
>>      
> If the iSCSI targets are actually block devices (lvm lvs, disk
> partitions, etc), than using FileIO is a mistake, it may bring up all
> kind of weird behaviours, though normally no real errors - though I
> don't really know how scst fares in this regard.
>
> My understanding : he planned to create a file on the mounted XFS
> volume with dd but instead he dd'ed the lv itself, which obviously
> destroyed the filesystem. Or something else, I don't really know :)
>
> Slawomir, please show us the scst config file. Did you use mkfs
> and dd on the target or the initiator? This isn't clear.
>
>    
It's my mistake in dd command, sorry for that.

First we mount the LV:

mount
[...]
/dev/vg+vg00/lv+i+lv0000 on /mnt/point type xfs 
(rw,nouuid,attr2,nobarrier,noquota)
[...]

then we run dd to file

dd if=/dev/zero of=/mnt/point/lun bs=1M conv=notrunc count=$size

$size is counted to leave some free space on the device

As the iSCSI target we use SCST 1.0.1.2. The scst.conf looks likes like 
this:

[HANDLER vdisk]
DEVICE 0QSP199WJI1yKOPj,/mnt/point/lun,WT,512,0QSP199WJI1yKOPj

[GROUP Default_iqn.2010-03:sn1.target0]
[GROUP Default]

[ASSIGNMENT Default_iqn.2010-03:sn1.target0]
DEVICE 0QSP199WJI1yKOPj,0
[ASSIGNMENT Default]

[TARGETS enable]

[TARGETS disable]

The problem is that we were able to use this LUN in the target, but 
suddenly after a reboot we are not.

Cheers
Slawek

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