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Re: Problem with file system on iSCSI FileIO

To: Christoph Hellwig <hch@xxxxxxxxxxxxx>
Subject: Re: Problem with file system on iSCSI FileIO
From: Emmanuel Florac <eflorac@xxxxxxxxxxxxxx>
Date: Fri, 24 Sep 2010 15:18:46 +0200
Cc: Slawomir Nowakowski <slawomir.nowakowski@xxxxxxxxxx>, Christoph Hellwig <hch@xxxxxxxxxxxxx>, Artur Piechocki <artur.piechocki@xxxxxxxxxx>, xfs@xxxxxxxxxxx, "'Ryszard Stawiarski'" <ryszard.stawiarski@xxxxxxxxxx>, ??ukasz Wittig <lukasz.wittig@xxxxxxxxxx>
In-reply-to: <20100924075505.GA24664@xxxxxxxxxxxxx>
Organization: Intellique
References: <4C9B5786.4010205@xxxxxxxxxx> <20100923143221.GA1989@xxxxxxxxxxxxx> <4C9B6B27.5050606@xxxxxxxxxx> <20100924075505.GA24664@xxxxxxxxxxxxx>
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.

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