Xen users - Sep 2007 - Image file or partitions over an iSCSI?

Dear all,

I will setup soon an Infortrend iSCSI SAN device with a raid6 volume and 
a DELL PE1950 (8 VMs) with a Qlogic iSCSI HBA (server to be duplicated 
at later time for redundancy).

My priorities are:

1) VMs on the iSCSI SAN in order to boot them also by another server if 
the first one fails

2) performances

3) live migration is a non mandatory option (i.e. I can suffer to 
shutdown machines and restart them with minor service interruption, 
maybe with a heartbeat script)

My questions are:

The server(s) will have a raid 1 with two 74GB sas 15krpm drives.
Where do you would store your VMs?
You would use partitions (i.e. a LUN for each VM) or images?
Swap files could be on the local disks?
Does a "local disk images and overnight mirror to the SAN" approach 
would be better in this case?

Religion question (optional...):

Waht would you prefere?

[ ] CentOS 5 with out of the box Xen
[ ] CentOS 5 with latest Xen
[ ] Debian 3.1 with latest Xen
[ ] Debian 4 with latest Xen

:-)

thank you anyway

	Ivan

P.S.
I''m available to perform tests on the above hardware if XenSource is 
interested, tell me what and how (from the 2nd week of October)
-- 
http://www.bio.dist.unige.it
voice: +39 010 353 2789
fax:   +39 010 353 2948

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Ivan Porro wrote:
>
> The server(s) will have a raid 1 with two 74GB sas 15krpm drives.
> Where do you would store your VMs?
> You would use partitions (i.e. a LUN for each VM) or images?
LUNs.
> Swap files could be on the local disks?
Yes, this will lead to better performance, but it will also prevent live
migration.
If you need live migration, use LUNs on SAN for swap as
well.
> Does a "local disk images and overnight mirror to the SAN"
approach
> would be better in this case?
>
For this to work you need to have snapshot, to make sure that the disk
images are consistent.
Generally I wouldn''t bother, just put your VMs on
SAN.
> Religion question (optional...):
>
> Waht would you prefere?
>
> [ ] CentOS 5 with out of the box Xen
> [ ] CentOS 5 with latest Xen
I''d go with CentOS.

As for Xen, depends on what you need. Out-of-the-box Xen will make
sysadmin task easier, as it will be part of the OS. It should work for
most scenarios, and it''s the one I''d recommend for general
use.

Latest Xen will get you more features (such as the ability tu run
Solaris domU on Linux dom0), but it will be somewhat harder on sysadmin
(imagine having 100 boxes, and you have to update Xen on all of them).

Regards,

Fajar

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Ivan Porro schrieb:
> Dear all,
> 
> I will setup soon an Infortrend iSCSI SAN device with a raid6 volume and 
> a DELL PE1950 (8 VMs) with a Qlogic iSCSI HBA (server to be duplicated 
> at later time for redundancy).
> 
> My priorities are:
> 
> 1) VMs on the iSCSI SAN in order to boot them also by another server if 
> the first one fails
> 
> 2) performances
> 
> 3) live migration is a non mandatory option (i.e. I can suffer to 
> shutdown machines and restart them with minor service interruption, 
> maybe with a heartbeat script)
> 
> My questions are:
> 
> The server(s) will have a raid 1 with two 74GB sas 15krpm drives.
> Where do you would store your VMs?
> You would use partitions (i.e. a LUN for each VM) or images?
> Swap files could be on the local disks?
Surely partitions, or better yet, LVM volumes for flexibility.
Images won''t allow you to do 1) (unless you set up and configure some 
fancy distributed fs).
Also, file images are not very good from the performance side, but also, 
data integrity (you are more likely to suffer a filesystem corruption if 
that filesystem is kept in a file).

If you keep swap on a local disk, you won''t be able to do a (live) 
migration.
You can keep swap on a dedicated partition/LVM volume (available via 
iSCSI), or just use a swapfile, on the guest iSCSI partition (ext3 etc.).

> Does a "local disk images and overnight mirror to the SAN"
approach
> would be better in this case?
Sounds like "no", but I''m not sure what you really mean by
the
"overnight mirror to the SAN".

> Religion question (optional...):
> 
> Waht would you prefere?
> 
> [ ] CentOS 5 with out of the box Xen
> [ ] CentOS 5 with latest Xen
> [ ] Debian 3.1 with latest Xen
> [ ] Debian 4 with latest Xen
I''d use the latest Xen, with the latest OS version. Debian or CentOS, 
doesn''t really matter I guess.


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