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Re: [Xen-users] Shared Storage

To: Jonathan Tripathy <jonnyt@xxxxxxxxxxx>
Subject: Re: [Xen-users] Shared Storage
From: Jonathan Dye <jdye@xxxxxxxxxxxxxxxxxxxxx>
Date: Sun, 24 Apr 2011 12:43:59 -0600 (MDT)
Cc: Xen List <xen-users@xxxxxxxxxxxxxxxxxxx>
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Let me pose it to you this way.  Say the queue depth is 32 for your iscsi-based 
PV, which would be pretty typical.  Would you want 'hundreds if not thousands' 
of vms sharing that same queue?

Also please note you will need a LOT of spindles to support a thousand VMs, 
unless you are doing diskless.  Is this a compute cluster or a 
consolidation/cloud project?

- Jonathan

----- Original Message -----
From: "Jonathan Tripathy" <jonnyt@xxxxxxxxxxx>
To: "Jonathan Dye" <jdye@xxxxxxxxxxxxxxxxxxxxx>, "Xen List" 
Sent: Sunday, April 24, 2011 12:31:33 PM
Subject: Re: [Xen-users] Shared Storage

We're talking houndreds, if not thousands of DomUs here. Will iSCSI on 
Linux scale to these large numbers?


On 24/04/2011 19:13, Jonathan Dye wrote:
> Why not create one iscsi lun per vm disk instead of carving them up on the 
> hypervisor?  That's more typical, and a more typical state of affairs in 
> linux is your friend.  Also, you would have just one lun queue if you 
> exported one big PV, instead of one lun queue per vbd. That becomes a problem 
> at scale.
> - Jonathan
> ----- Original Message -----
> From: "Jonathan Tripathy"<jonnyt@xxxxxxxxxxx>
> To: "Xen List"<xen-users@xxxxxxxxxxxxxxxxxxx>
> Sent: Sunday, April 24, 2011 11:25:38 AM
> Subject: [Xen-users] Shared Storage
> Hi Everyone,
> I am consider such a setup where I export an iSCSI target to a Xen node.
> This Xen node will then use the iSCSI block device as an LVM PV, and
> create lots of LVs for DomU use.
> I was wondering if anyone could make me aware of any special
> consideration I would need to take. I've posted a similar question to
> the LVM list to ask for further tips more specific to LVM.
> Am I barking down the wrong path here? I know it would be very easy to
> just an NFS server and use image files, but this will be for a large
> scale DomU hosting so this isn't really an option. Additionally, if I
> wanted to make the LVM VG visible to multiple Xen nodes, is it just a
> matter of running CLVM on each Xen node? Please keep in mind that only
> one Xen node will be using an LV at any one time (so no need for GFS, I
> believe)
> Any help or tips would be appreciated
> Thanks
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