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From Nitin Mehta <Nitin.Me...@citrix.com>
Subject Re: XenServer & VM Snapshots
Date Tue, 04 Dec 2012 08:16:43 GMT

On 04-Dec-2012, at 12:44 PM, Marc Cirauqui wrote:

If I may, we've detected very poor performance executing snapshots.

We think it's due to XenServer's API, I don't know how and why, but the API
is very slow and runs one task at a time (if it is doing paralelization
it's almost nothing).

Do you know if there's a way to improve IO rates on XS side?

thx.


Marc - I think there has been some work from the CS side as well to better the performance
a bit. I think following work has been done. You can tweak the parameter concurrent.snapshots.threshold.perhost
 a bit to achieve some better performance based on the workload.
More info @ https://cwiki.apache.org/confluence/display/CLOUDSTACK/Snapshot+improvements+FS



On Mon, Dec 3, 2012 at 8:07 PM, Matthew Hartmann <mhartmann@tls.net<mailto:mhartmann@tls.net>>
wrote:

Thank you Anthony! :)

Cheers,

Matthew



Matthew Hartmann
Systems Administrator | V: 812.378.4100 x 850 | E: mhartmann@tls.net<mailto:mhartmann@tls.net>

TLS.NET<http://TLS.NET>, Inc.
http://www.tls.net


-----Original Message-----
From: Anthony Xu [mailto:Xuefei.Xu@citrix.com]
Sent: Monday, December 03, 2012 1:59 PM
To: 'Cloudstack Developers'; cloudstack-users@incubator.apache.org<mailto:cloudstack-users@incubator.apache.org>
Subject: RE: XenServer & VM Snapshots

CS 3.0.2 is too old version.

I'm pretty sure mount & copy on the same host in 3.0.4 and 3.0.5.
If mount & copy might be on different hosts, the issue is very likely to
happen.
I didn't hear this issue from QA and users.

I just checked vmopsSnapshot plug-in for XenServer, at /etc/xapi.d/plugins,
Which mounts secondary storage just before sparse-dd.

I recommend you to upgrade new version.

If you still see the issue,

Please post related management server log and /var/log/SMlog in XenServer.


Anthony











-----Original Message-----
From: Matthew Hartmann [mailto:mhartmann@tls.net]
Sent: Monday, December 03, 2012 10:31 AM
To: cloudstack-users@incubator.apache.org<mailto:cloudstack-users@incubator.apache.org>
Cc: 'Cloudstack Developers'
Subject: RE: XenServer & VM Snapshots

Anthony:

Thank you for the prompt and informative reply.

I'm pretty sure mount and copy are using the same XenServe host.

The behavior I have witnessed with CS 3.0.2 is that it doesn't always
do the
mount & copy on the same host. Out of the 12 tests I've performed, only
once
was the mount & copy performed on the same host that the VM was running
on.

I think the issue is the backup takes a long time because the data
volume
is big and network rate is low.
You can increase "BackupSnapshotWait" in global configuration table
to let
the backup operation finish.

I increased this in global settings from the default of 9 hours to 16
hours.
The snapshot still doesn't complete on time; it on average copies about
~460G before it times out. I'm pretty confident the network rate isn't
the
bottle neck as ISOs and imported VHDs install quickly. We have the
Secondary
Storage server set as the only internal site allowed to host files. I
upload
my ISO or VHD to Secondary Storage server and install using SSVM which
completes in a very timely manner. With a 1Gb network link, 1TB should
copy
in roughly 2 hours (if the link is saturated by the copy process); I've
only
found snapshotting (template creation appears to work flawlessly) to
take an
insanely long time to complete.

Is there anything else I can do to increase performance or logs I
should
check?

Cheers,

Matthew


Matthew Hartmann
Systems Administrator | V: 812.378.4100 x 850 | E: mhartmann@tls.net<mailto:mhartmann@tls.net>

TLS.NET<http://TLS.NET>, Inc.
http://www.tls.net


-----Original Message-----
From: Anthony Xu [mailto:Xuefei.Xu@citrix.com]
Sent: Monday, December 03, 2012 12:31 PM
To: Cloudstack Users
Cc: Cloudstack Developers
Subject: RE: XenServer & VM Snapshots

Hi Matthew,

You analysis is correct except following,

I must mention that the same Compute Node that ran sparse_dd or
mounted
Secondary Storage is not always the same. It appears the Management
Server
is simply round-robining through the list of >Compute Nodes and using
the
first one that is available.

I'm pretty sure mount and copy are using the same XenServe host.

I think the issue is the backup takes a long time because the data
volume is
big and network rate is low.
You can increase "BackupSnapshotWait" in global configuration table to
let
the backup operation finish.


Since CS takes the advantage of XenServer image format VHD, it uses VHD
to
do snapshot and clone, it requires snapshot to be backed up through
XenServer host.
The ideal solution for this issue might be leverage storage snapshot
and
clone functionality, Then snapshot back up is executed by storage host,
relieve some of the limitation.
Currently CS doesn't support this,  it is not hard to support this
after
Edison finishes storage frame change, it should be just another storage
plug-in.
When CS uses storage server snapshot and clone function, CS needs to
consider number of snapshot , number of volume limitation of storage
server.


Anthony














From: Matthew Hartmann [mailto:mhartmann@tls.net]
Sent: Monday, December 03, 2012 9:08 AM
To: Cloudstack Users
Cc: Cloudstack Developers
Subject: XenServer & VM Snapshots

Hello! I'm hoping someone can help me troubleshoot the following issue:

I have a client who has a 960G data volume which contains their VM's
Exchange Data Store. When starting a snapshot, I found that a process
is
started on one of my Compute Nodes titled "sparse_dd". I found that
this
process is then sending the output of "sparse_dd" through another
Compute
Node's xapi before placing it into the "snapshot store" on Secondary
Storage. It appears that this is part of the bottle neck as all of our
systems are connected via gigabit link and should not take 15+ hours to
create a snapshot. The following is the behavior that I have analyzed
from
within my environment:


1)     Snapshot is started (either via Manual or Scheduled).

2)     Compute Node 1 "processes the snapshot" by exposing the VDI
which
"sparse_dd" then creates a "thin provisioned" snapshot.

3)     The output of sparse_dd is delivered over HTTP to xapi on
Compute
Node 2 where the Management Server mounted Secondary Storage.

4)     Compute Node 2 (receiving the snapshot via xapi) stores the
snapshot
in the Secondary Storage mount point.

Based on the behavior, I have devise the following logic that I believe
CloudStack is utilizing:


1)     CloudStack creates a "snapshot VDI" via XenServer Pool Master's
API.

2)     CloudStack finds a Compute Node that can mount Secondary Storage.

3)     CloudStack finds a Compute Node that can run "sparse_dd".

4)     CloudStack uses available Compute node to output the VDI to xapi
on
the Compute Node that mounted Secondary Storage.

I must mention that the same Compute Node that ran sparse_dd or mounted
Secondary Storage is not always the same. It appears the Management
Server
is simply round-robining through the list of Compute Nodes and using
the
first one that is available.

Does anyone have any input on the issue I'm having or analysis of how
CloudStack/XenServer snapshots operate?

Thanks!

Cheers,

Matthew



Matthew Hartmann
Systems Administrator | V: 812.378.4100 x 850 | E: mhartmann@tls.net<mailto:mhartmann@tls.net>

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