iSCSI, RDM and usage of SAN features likes snapshots

[Anders_Gregerse]

I'm trying to use RDM's with my vmware certified SAN (Equallogic), but I can't use the vendors client software to create snapshots. According to the SAN vendor it is because that vmware strips the "Vendor Specific Page", so they can't identify their storage system. The SAN vendor recommends using the Microsoft iSCSI software initiator inside the guest, but that works against the design of RDMs and will use the "data" nics instead of the iSCSI hbas and I consider the usage of Microsoft iSCSI software initiator a security risk that could allow for a denial of service attack against all iSCSI devices. Using Physical or Virtual mode doesn't make a difference.

Are there anyone else that have the same problem with their iSCSI based SAN (other than Equallogic)?

[chris_delaney]

Hi Anders,

I have just invested in an EqualLogic SAN and have been battling with exactly the same problem. Unfortunately there doesn't seem to be an easy way around this at the moment, although EqualLogic have assured me that they have a vmware-aware snapshotting tool in the pipeline. The current method I'm looking at implementing is as follows:

- System disks run on normal VMFS volumes from the SAN.

- Data disks for databases on Microsoft iSCSI initiator-attached NTFS volumes from the SAN. Using this method provides access for the EqualLogic HIT to the databases - the latest version of which can do SQL Server 2005 snapshots and recovery.

- For our main file server I plan to have a very small 'stub' Windows VM with some iSCSI Initiator volumes being shared with the normal Windows functionality.

I have ensured that the SAN traffic is on a physically separate network to everything else. This means that I can have a virtual switch on each ESX host which has the iSCSI vmkernal, service console and virtual machine port groups on. That way I can minimise the amount of additional work that the VMs have to do as a result of using the Microsoft iSCSI Initiator. The corporate LAN and SAN traffic is kept absolutely separate.

From a backup perspective I've been having good results with VCB and plan to start using it for full VM backups fairly shortly. I agree that RDMs are the probably the best way to do this for performance but I have to say that I've seen no degredation in service using the iSCSI initiator inside VMs. For peace of mind I've been taking manual EqualLogic snapshots of all the VMs at a time when they can be suspended without causing any problems to users.

Let me know if you have any luck with the RDMs.

Chris

[Anders_Gregerse]

Hi Chris,

Interesting information. Assuming that you use iSCSI HBAs for the vmfs traffic, do you use separate NICs for the Microsoft iSCSI SAN traffic or do that run over the same NICs as your other "data" port groups (separated with VLANs of course).

VCB is the next thing I have to look at.

[chris_delaney]

Hi Anders,

I'm running all the iSCSI traffic (both VMWare and Windows) through the same NICs - I have 2 in each ESX host.

Cheers.

Chris

[gparker]

Hi Chris,

I too have an EqualLogic SAN and am contemplating using the iscsi initiator within my VM's to acess the VMs data volumes so that I can use the HIT tools to create snapshots. Will I be able to VMotion these VM's from one ESX host to another?

Regards,

George.

[happyhammer]

George

yes you will be able to vMotion from one host to another and you will also find you get far better disk performance from the iSCSI initiator inside a vm than using the Hardware HBA,

[gparker]

Thanks happyhammer :smileyblush:

Regards,

George.