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Re: Problem with file system on iSCSI FileIO

To: Emmanuel Florac <eflorac@xxxxxxxxxxxxxx>, Christoph Hellwig <hch@xxxxxxxxxxxxx>
Subject: Re: Problem with file system on iSCSI FileIO
From: Slawomir Nowakowski <slawomir.nowakowski@xxxxxxxxxx>
Date: Fri, 24 Sep 2010 15:49:10 +0200
Cc: xfs@xxxxxxxxxxx, Artur Piechocki <artur.piechocki@xxxxxxxxxx>, Łukasz Wittig <lukasz.wittig@xxxxxxxxxx>, "'Ryszard Stawiarski'" <ryszard.stawiarski@xxxxxxxxxx>
In-reply-to: <20100924151846.1208611c@xxxxxxxxxxxxxxxxxxxx>
Organization: Open-E
References: <4C9B5786.4010205@xxxxxxxxxx> <20100923143221.GA1989@xxxxxxxxxxxxx> <4C9B6B27.5050606@xxxxxxxxxx> <20100924075505.GA24664@xxxxxxxxxxxxx> <20100924151846.1208611c@xxxxxxxxxxxxxxxxxxxx>
Reply-to: slawomir.nowakowski@xxxxxxxxxx
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Dear Sirs,
Le Fri, 24 Sep 2010 03:55:05 -0400
Christoph Hellwig<hch@xxxxxxxxxxxxx>  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:

/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 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]

[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.


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