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Re: [Xen-users] Shared Storage

To: Jonathan Dye <jdye@xxxxxxxxxxxxxxxxxxxxx>
Subject: Re: [Xen-users] Shared Storage
From: Bart Coninckx <bart.coninckx@xxxxxxxxxx>
Date: Sun, 24 Apr 2011 22:04:56 +0200
Cc: xen-users@xxxxxxxxxxxxxxxxxxx, Jonathan Tripathy <jonnyt@xxxxxxxxxxx>
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I concur, in terms of performance Linux based iSCSI might not be the fastest, but in terms of what you are familiar with or what is flexible, it might be a good choice again.

Also it might be worth to look into ATAoE. Not popular, but I'm told it is fast as hell.


On 04/24/11 22:01, Jonathan Dye wrote:
So, linux storage servers then.  If I might interject again I would suggest you 
try nexenta or solaris 11 express.  If not, try a NAS appliance like FreeNAS or 
Openfiler - one of the linux based ones is likely to have done a better job 
than you will attempting to reproduce it.  If you're brave try clustered 
storage with Ceph since that's the way everything is headed anyways (i.e. the 
way of isilon, luster, GPFS and the like).  After all reasonable options fail, 
roll your own with LVM.  IMO, making a storage server out of linux is inferior 
because the volume management, filesystem, and raid are stratified instead of 
engineered together.  If you use any modern solaris kernel based distribution, 
like the ones named above, and ZFS then I think you'll find that it can fill 
your network connection with storage traffic without tweaking.  The downside is 
you have to be careful about hardware selection.

- Jonathan

----- Original Message -----
From: "Jonathan Tripathy"<jonnyt@xxxxxxxxxxx>
To: "Bart Coninckx"<bart.coninckx@xxxxxxxxxx>, xen-users@xxxxxxxxxxxxxxxxxxx
Sent: Sunday, April 24, 2011 1:43:46 PM
Subject: RE: [Xen-users] Shared Storage

Thanks Bart. Very helpful info

I agree with you about the LVM PV issue. It is indeed very uncomfortable. I am 
looking into CLVM (Cluster LVM) though, however this isn't very well documented.

So the current idea is one target per Xen node (hense one target per RAID array 
on the storage server), and one LUN per DomU. Is it easy enough to expand and 
shrink LUNs? This was the advantage of LVM that I loved. I guess I would run 
LVM on the storage server and export the LVs?


-----Original Message-----
From: Bart Coninckx [mailto:bart.coninckx@xxxxxxxxxx]
Sent: Sun 24/04/2011 20:40
To: Jonathan Tripathy
Cc: Jonathan Dye; Xen List
Subject: Re: [Xen-users] Shared Storage

I think you better take one target and then several LUNs on it (one per
DomU), that would make more sense. If you don't do that and use just one
LUN for several DomU's, you need to create PVM LV's on the newly created
disk for each DomU on the hypervisor side, does not really sound
comfortable. You would also close any path to HA, unless you maybe
introduce some locking system, since every hypervisor would be wanting
to try to write to the LUN.


On 04/24/11 21:35, Jonathan Tripathy wrote:
Hi Guys,

Please forget the "thousands" number. We would have thousands of DomUs,
but this would be spread over multiple storage servers, so never mind
about that scale.

If I was exporting "One big LUN" per Xen node, it would contain at most
80 DomU LVs (In real world usage, closer to 50). Furthermore, each LUN
would be exported from a seperate RAID array. Each storage server would
contain x number of RAID arrays, where x equals the number of Xen nodes
and the number of exported LUNs.

Of course, if I went with one LUN per DomU, then each storage server
would contain 80x LUNs (closer to 50x though).

With these numbers, any idea which is better?


-----Original Message-----
From: Bart Coninckx [mailto:bart.coninckx@xxxxxxxxxx]
Sent: Sun 24/04/2011 19:36
To: Jonathan Tripathy
Cc: Jonathan Dye; Xen List
Subject: Re: [Xen-users] Shared Storage

That is completely dependent on your hardware specs and DomU's properties.
It sounds like a lot though. I seem to remember some time ago you also
stated to want to run at least 100 DomUs on one hypervisor, maybe this
is again pushing it.
With a decent RAID and 10gbit or infiniband you can go a long way
though. You should also consider using SCST instrad of IET as it is faster.


On 04/24/11 20:31, Jonathan Tripathy wrote:
  >  We're talking houndreds, if not thousands of DomUs here. Will iSCSI on
  >  Linux scale to these large numbers?
  >  Thanks
  >  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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