Best practices questions

[Lopez, Denise]

Hi all,

I am in the process of building a new Xen server from scratch and wanted
to ask a couple of questions about best practices.

First, should the guest domains be image files or LVM's or just regular
ext3 partitions? What are the pros and/or cons of each?

Second,  since the Dom0 is supposed to be kept secure, and most of my
servers I don't install any X11 server on, is there any security risk
installing an X11 server on the Dom0 in order to take advantage of the
virt-manager GUI interface?

Thank you in advance for any thoughts and or opinions.

Denise Lopez

UCLA - Center for Digital Humanities

Network Services

Linux Systems Engineer

337 Charles E. Young Drive East

PPB 1020

Los Angeles, CA 90095-1499

310/206-8216

[Stephen John Smoogen]

On Nov 28, 2007 5:31 PM, Lopez, Denise  wrote:
> Hi all,
>
> I am in the process of building a new Xen server from scratch and wanted to
> ask a couple of questions about best practices.
>
> First, should the guest domains be image files or LVM's or just regular ext3
> partitions? What are the pros and/or cons of each?

Are you talking about inside the guests or where the guests are in DomO?

For the guests files on Dom0, I am using image files stored on DomO's
LVM.. though I may follow some howtos on shared storage so that
failover works in the future.

Inside the guests, I am using ext3 direct in the image versus using
LVM+ext3. I wanted things to be simple to understand for myself.
> Second,  since the Dom0 is supposed to be kept secure, and most of my
> servers I don't install any X11 server on, is there any security risk
> installing an X11 server on the Dom0 in order to take advantage of the
> virt-manager GUI interface?

I do not know of any major security issues... but you should use
security in depth.
1) secure the logins
2) firewall the machine so that only ssh X port forwarding is available
3) keep the system up-2-date.
4) follow other best practices for securing a system.

[Lopez, Denise]

Are you talking about inside the guests or where the guests are in DomO?

I was talking about where the guests are in Dom0.

Denise Lopez

-----Original Message-----
From: Stephen John Smoogen [mailto:[e-mail]] 
Sent: Wednesday, November 28, 2007 4:39 PM
To: Lopez, Denise
Cc: [e-mail]
Subject: Re: [Fedora-xen] Best practices questions

On Nov 28, 2007 5:31 PM, Lopez, Denise  wrote:
> Hi all,
>
> I am in the process of building a new Xen server from scratch and

wanted to
> ask a couple of questions about best practices.
>
> First, should the guest domains be image files or LVM's or just

regular ext3
> partitions? What are the pros and/or cons of each?

Are you talking about inside the guests or where the guests are in DomO?

For the guests files on Dom0, I am using image files stored on DomO's
LVM.. though I may follow some howtos on shared storage so that
failover works in the future.

Inside the guests, I am using ext3 direct in the image versus using
LVM+ext3. I wanted things to be simple to understand for myself.
> Second,  since the Dom0 is supposed to be kept secure, and most of my
> servers I don't install any X11 server on, is there any security risk
> installing an X11 server on the Dom0 in order to take advantage of the
> virt-manager GUI interface?

I do not know of any major security issues... but you should use
security in depth.
1) secure the logins
2) firewall the machine so that only ssh X port forwarding is available
3) keep the system up-2-date.
4) follow other best practices for securing a system.

[Dustin Henning]

Denise,
    Personally, I recommend lvm or partitions in Dom0 vs image files for
performance reasons.  The choice to use LVM or partitions can really safely
be left to whichever you are more comfortable with.  If you want to be able
to resize DomUs, then lvm might be useful, but if that can be done, it is
probably quite complicated.
    Dustin

-----Original Message-----
From: [e-mail] [mailto:[e-mail]]
On Behalf Of Lopez, Denise
Sent: Wednesday, November 28, 2007 19:43
To: [e-mail]
Subject: RE: [Fedora-xen] Best practices questions

Are you talking about inside the guests or where the guests are in DomO?

I was talking about where the guests are in Dom0.

Denise Lopez

-----Original Message-----
From: Stephen John Smoogen [mailto:[e-mail]] 
Sent: Wednesday, November 28, 2007 4:39 PM
To: Lopez, Denise
Cc: [e-mail]
Subject: Re: [Fedora-xen] Best practices questions

On Nov 28, 2007 5:31 PM, Lopez, Denise  wrote:
> Hi all,
>
> I am in the process of building a new Xen server from scratch and

wanted to
> ask a couple of questions about best practices.
>
> First, should the guest domains be image files or LVM's or just

regular ext3
> partitions? What are the pros and/or cons of each?

Are you talking about inside the guests or where the guests are in DomO?

For the guests files on Dom0, I am using image files stored on DomO's
LVM.. though I may follow some howtos on shared storage so that
failover works in the future.

Inside the guests, I am using ext3 direct in the image versus using
LVM+ext3. I wanted things to be simple to understand for myself.
> Second,  since the Dom0 is supposed to be kept secure, and most of my
> servers I don't install any X11 server on, is there any security risk
> installing an X11 server on the Dom0 in order to take advantage of the
> virt-manager GUI interface?

I do not know of any major security issues... but you should use
security in depth.
1) secure the logins
2) firewall the machine so that only ssh X port forwarding is available
3) keep the system up-2-date.
4) follow other best practices for securing a system.

[Markus Armbruster]

"Lopez, Denise"  writes:
> Hi all,
>
> I am in the process of building a new Xen server from scratch and wanted
> to ask a couple of questions about best practices.
>
> First, should the guest domains be image files or LVM's or just regular
> ext3 partitions? What are the pros and/or cons of each?

Image files are slow.  Sparse image files lead to *nasty* domU data
corruption when you run out of space in the filesystem containing the
image file.

LVM vs. regular partitions is the usual deal: LVM gives you more
flexibility.  You might find that you appreciate the flexibility even
more when you run guests.
> Second,  since the Dom0 is supposed to be kept secure, and most of my
> servers I don't install any X11 server on, is there any security risk
> installing an X11 server on the Dom0 in order to take advantage of the
> virt-manager GUI interface?

X is network transparent.  Why not use a remote display?  You don't
need an X server in dom0 for that.
> Thank you in advance for any thoughts and or opinions.
>
> Denise Lopez

[Daniel P. Berrange]

On Mon, Dec 03, 2007 at 10:48:59AM +0100, Markus Armbruster wrote:
> "Lopez, Denise"  writes:
> > Hi all,
> >
> > I am in the process of building a new Xen server from scratch and wanted
> > to ask a couple of questions about best practices.
> >
> > First, should the guest domains be image files or LVM's or just regular
> > ext3 partitions? What are the pros and/or cons of each?
>
> Image files are slow.  Sparse image files lead to *nasty* domU data
> corruption when you run out of space in the filesystem containing the
> image file.

Actually that's not true. You will definitely get I/O errors in the
DomU if Dom0 runs out of space. Journalling FS will save you though.
If you kill the guest, add more Dom0 space, and start the guest again
it should recover just fine. This is why I went to great lengths to
fixing Xen 3.0.3 to make sure I/O errors are actually propagated to 
the guest, rather than being dropped on the floor in Dom0 pretending
it was all OK like in the bad Xen 3.0.2 days.

The issue with sparse files is that they have really bad performance
characteristics whe nyou do writes, becaue each time Dom0 as to allocate
an extra block behind the sparse file it hits the journal, and this 
basically serializes all I/O requests in the guest. Once the sparse
file is fully-allocated, it should be good again.
> LVM vs. regular partitions is the usual deal: LVM gives you more
> flexibility.  You might find that you appreciate the flexibility even
> more when you run guests.

LVM & partitions give best performance characteristics.

Regards,
Dan.

[Aaron Metzger]

Daniel P. Berrange wrote:
> > LVM vs. regular partitions is the usual deal: LVM gives you more
> > flexibility.  You might find that you appreciate the flexibility even
> > more when you run guests.
>
> LVM & partitions give best performance characteristics.
>
> Regards,
> Dan.

Dan:

Thanks for your insight.

If, for example, a guest has separate /root, /boot, and swap do you 
recommend as best practice a separate logical volume for each or do you 
give just one logical volume to the guest for it to dice up into the 
various types of file systems?  Is there a significant performance 
difference between these two solutions?

For us newbies using virt-install or virt-manager, it prompts for at 
most one partitition (which can be a logical volume) so without editing 
of the config after the fact it naturally leads to the case of using 
just one logical volume for the entire guest with it dicing it up into 
/root, /boot, and swap or whatever.

So, for the case of just one logical volume which has been "formatted" 
during the guest install, this led to the question of how do I 
generically backup and restore that one logical volume.

Every piece of documentation that I find for creating an LVM snapshot 
and then creating a backup requires that the snapshot volume be mounted 
to perform the backup.  This led me on an adventure with device mapper 
and kpartx etc during which I was able to eventually get to and backup 
the inner guts of my guest but it seemed like there had to be a better way.

Is there a vanilla generic backup and restore procedure for a logical 
volume (a snapshot volume of the running guest logical volume) which 
does not require case-by-case knowledge of what type of file system(s) 
have been mapped to that logical volume?  If so, is there then also a 
way to do that backup in a manner which only stores the small amount of 
space actually used by the guest instead of the entire space allocated 
to the logical volume?  In other words, something that preserves the 
idea of sparseness?  This is probably a generic LVM question but I could 
not find my answer in the LVM docs either.

My lack of knowledge related to the above questions is why I am 
currently using image files but would love to switch to individual 
logical volumes for the performance benefits.

--
Thanks,
Aaron