XenServer Pool and iSCSI

[zundero]

Hello Forum,

I was setting up the shared storage repositories (SR) of a XenServer pool on FreeNAS iSCSI targets.
First simple tests worked fine.

According to http://wiki.freenas.org/index.php/ISCSI#Initiators

"A clustered filesystem is required on the block device" or
"care must be taken that only one initiator at a time has read/write access"

QNAP is talking here: http://www.qnap.com/en/index.php?lang=en&sn=2712
about iSCSI advanced ACL in a clustered network environment.

That's confusing.
I cannot find out if XenServer is using a clustered file system. I know SRs are LVM.
Is XenMotion and FreeNAS handling this correctly? Does somebody run this in production?

many thanks in advance, zundero

 

[jgreco]

Let me fully quote that out for you, because I think you missed a few words:

"A clustered filesystem is required on the block device" or
"If a traditional filesystem [...] care must be taken that only one initiator at a time has read/write access"

What it is saying is that if you have two traditional filesystems on two hosts both thinking that this is their own private disk, much entertainment will be had tomorrow when each has made their own private changes to the shared disk and you lose all your data.

You have to figure out if whatever you are using is a clustered filesystem.

From the term "Shared Storage Repositor[y]", my guess is yes.

Based on this article here, my guess is again yes.

Since most virtualization technology is oriented towards being able to shuffle workloads around, it would strike me as odd if you were using a standard Xen SAN subsystem and it didn't support sharing, so ultimately my guess is still yes.

Since I don't currently do Xen and it's your data, you are encouraged not to rely solely on my guesses or quick read of the documentation. Fortunately, you seem to be reading documentation so you're likely to figure it out.

 

[zundero]

Thank's a lot jgreco.

Excellent article:

Based on this article here, my guess is again yes.

As far as I can see FreeNAS supports LVMoiSCSI (LVM over iSCSI)

Code:

[root@naxensrv ~]# xe sr-list type=lvmoiscsi
...
uuid ( RO)                : 4f686d67-7698-ce0b-38c4-64e91d5745da
          name-label ( RW): NAOS1-iSCSI
    name-description ( RW): iSCSI SR [192.168.246.21 (iqn.freenas.wlb.at.istgt:naos1)]
                host ( RO): naxensrv
                type ( RO): lvmoiscsi
        content-type ( RO):
...

So now I have to check out that LVMoiSCSI is definitly a clustered filesystem.

 

[zundero]

So now I have to check out that LVMoiSCSI is definitly a clustered filesystem.

No it's not...
This article http://virtualizationreview.com/blo...orage-note-for-netapp-equallogic-devices.aspx says

Citrix's perspective is not to build a clustered file system, but to let the storage product's APIs be utilized for optimal performance.

But; Peter's (from Italy) comment explains

Hmmm, but XenServer uses a clustered version of LVM to provide the same type of functionality as VMFS provides, without using a filesystem. Which includes among others fast cloning, snapshotting etc, all in the base (free) version. All the work is done by the hypervisor layer instead of the storage subsystem as in the case of Essentials for XenServer.

Means, I am trusting XenServer's hypervisor layer.