#26 - xl: require explicit action to share a disk between vms

Owner: Ian Campbell <Ian.Campbell@citrix.com>

Date: Thu Dec 19 14:15:01 2013

Last Update: Thu Dec 19 14:15:01 2013

Severity: wishlist

Affects:

State: Open

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From: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
To: George Dunlap <George.Dunlap@eu.citrix.com>
Cc: "xen-devel@lists.xen.org" <xen-devel@lists.xen.org>
Subject: Re: [Xen-devel] Xen 4.4 development update: Is PVH a blocker?
Date: Fri, 13 Dec 2013 14:43:26 -0500
Message-ID: <20131213194326.GA28712@phenom.dumpdata.com>

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> == Open ==
>
Also, xl as opposed to xend, allows me to share a disk without
any fanfare.

Meaning I can do this:

xl block-attach phy:/dev/sda latest1 xvda w
xl block-attach phy:/dev/sda latest2 xvda w

while if I had used 'xend' I had to also append the '!' parameter
to denote it as 'shared'.


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From: George Dunlap <george.dunlap@eu.citrix.com>
To: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Cc: "xen-devel@lists.xen.org" <xen-devel@lists.xen.org>
Subject: Re: [Xen-devel] Xen 4.4 development update: Is PVH a blocker?
Date: Mon, 16 Dec 2013 10:50:54 +0000
Message-ID: <52AEDB0E.30707@eu.citrix.com>

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On 12/13/2013 07:43 PM, Konrad Rzeszutek Wilk wrote:
>> == Open ==
>>
> Also, xl as opposed to xend, allows me to share a disk without
> any fanfare.
>
> Meaning I can do this:
>
> xl block-attach phy:/dev/sda latest1 xvda w
> xl block-attach phy:/dev/sda latest2 xvda w
>
> while if I had used 'xend' I had to also append the '!' parameter
> to denote it as 'shared'.

Is xl intended to have that level of information?  The 'l' originally 
meant "light".

  -George

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From: Ian Campbell <Ian.Campbell@citrix.com>
To: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Cc: "xen-devel@lists.xen.org" <xen-devel@lists.xen.org>, George Dunlap <George.Dunlap@eu.citrix.com>
Subject: Re: [Xen-devel] Xen 4.4 development update: Is PVH a blocker?
Date: Mon, 16 Dec 2013 10:54:17 +0000
Message-ID: <1387191257.20076.70.camel@kazak.uk.xensource.com>

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On Fri, 2013-12-13 at 14:43 -0500, Konrad Rzeszutek Wilk wrote:
> > == Open ==
> >
> Also, xl as opposed to xend, allows me to share a disk without
> any fanfare.
> 
> Meaning I can do this:
> 
> xl block-attach phy:/dev/sda latest1 xvda w
> xl block-attach phy:/dev/sda latest2 xvda w
> 
> while if I had used 'xend' I had to also append the '!' parameter
> to denote it as 'shared'.

Do you find that restriction to be valuable in practice?

Was it ever reliable? How did it cope with /dev/mapper/FOO-BAR
vs /dev/FOO/BAR and other similar aliases (/dev/cdrom etc)?

We could certainly cause xl to swallow the '!' for compatibility but is
the feature itself necessary?

I have a feeling this is mostly implemented by checks in the block
scripts rather than the toolstack itself, perhaps libxl drives them a
bit differently.

Ian.


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From: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
To: Ian Campbell <Ian.Campbell@citrix.com>
Cc: George Dunlap <George.Dunlap@eu.citrix.com>, "xen-devel@lists.xen.org" <xen-devel@lists.xen.org>
Subject: Re: [Xen-devel] Xen 4.4 development update: Is PVH a blocker?
Date: Mon, 16 Dec 2013 10:10:41 -0500
Message-ID: <20131216151041.GA14186@phenom.dumpdata.com>

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On Mon, Dec 16, 2013 at 10:54:17AM +0000, Ian Campbell wrote:
> On Fri, 2013-12-13 at 14:43 -0500, Konrad Rzeszutek Wilk wrote:
> > > == Open ==
> > >
> > Also, xl as opposed to xend, allows me to share a disk without
> > any fanfare.
> > 
> > Meaning I can do this:
> > 
> > xl block-attach phy:/dev/sda latest1 xvda w
> > xl block-attach phy:/dev/sda latest2 xvda w
> > 
> > while if I had used 'xend' I had to also append the '!' parameter
> > to denote it as 'shared'.
> 
> Do you find that restriction to be valuable in practice?

It protects me from doing silly mistakes.
> 
> Was it ever reliable? How did it cope with /dev/mapper/FOO-BAR
> vs /dev/FOO/BAR and other similar aliases (/dev/cdrom etc)?

I am not sure - but it did work across device mapper.
> 
> We could certainly cause xl to swallow the '!' for compatibility but is
> the feature itself necessary?

Not for Xen 4.4.
> 
> I have a feeling this is mostly implemented by checks in the block
> scripts rather than the toolstack itself, perhaps libxl drives them a
> bit differently.

I can do some investigation for this. After New Year though.

> 
> Ian.
> 

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From: Ian Campbell <Ian.Campbell@citrix.com>
To: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Cc: George Dunlap <George.Dunlap@eu.citrix.com>, "xen-devel@lists.xen.org" <xen-devel@lists.xen.org>
Subject: Re: [Xen-devel] Xen 4.4 development update: Is PVH a blocker?
Date: Thu, 19 Dec 2013 14:06:02 +0000
Message-ID: <1387461962.9925.82.camel@kazak.uk.xensource.com>

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create ^
title it xl: require explicit action to share a disk between vms
severity it wishlist
thanks

On Fri, 2013-12-13 at 14:43 -0500, Konrad Rzeszutek Wilk wrote:
> > == Open ==
> >
> Also, xl as opposed to xend, allows me to share a disk without
> any fanfare.
> 
> Meaning I can do this:
> 
> xl block-attach phy:/dev/sda latest1 xvda w
> xl block-attach phy:/dev/sda latest2 xvda w
> 
> while if I had used 'xend' I had to also append the '!' parameter
> to denote it as 'shared'.
> 
> 
> _______________________________________________
> Xen-devel mailing list
> Xen-devel@lists.xen.org
> http://lists.xen.org/xen-devel



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