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Saturday, January 15, 2011

RHEV Storage Explained

RHEV Storage Related Frequently Asked Questions

What are all the storage types supported on RHEV? 
ATM current RHEV2.2 Release supports only three storage types  NFS,ISCSI and FCP . 
 How the Virtual Machine Images are Stored if the storage is NFS,ISCSI or FCP on RHEV ?

  If you use NFS , all the disk are stored in a file format , and for ISCSI or FCP Storage it will set up a VG on the LUN, partition to LVs as needed and present those to the Virtual Machine as Hard Disk. 

How to debug  or to clean a disk in case of ISCSI or FCP LUN Where  the VolumeGroup  which is initialized for part but could not be used  while attaching a Storage Domain from RHEV Manager?

 If it is added to RHEV-M, all you need to do is remove it so  it will remove the RHEV signatures from the LUN.
Otherwise you can either destroy the target and recreate it completely from the FCP or ISCSI box side. So that wedon't destroy LUNs that shouldn't have been presented to RHEV by mistake .

Do below with very carefully  at your own  risk to avoid accidental  removal of  any existing active VG's and LV'S

 If removing or recreating the LUN from the SAN or ISCSI is not possible You can use the fidsk -l and  iscsi tools, for iscsi see ( for mounting the volume  and use vgscan vgremove for cleaning it up from the rhev-h side, or simply push some zeros using  dd of=/dev/zero 4KB of Zeros to the device and it need host reboot
Is it possible or is there an option to turn off multipath on RHEV Hypervisors?
Multipath cannot be turned off, it's how VDSM(agent running on RHEV-H) enumerates storage,without it, there's no fiber channel or iSCSi, its used even on single path systems. 
What is the difference between "Preconfigured vs Build New Domain" while attaching a new Storage Domain on RHEV ?
No difference whatsoever.  The only reason "preconfigured" is there is because many organizations are used to having their storage people set up everything storage related (up to VG level) so in that case you can use the preconfigured or if you want to RHEV to create a Volume Group on top of the LUN you presented from ISCSI or FCP then you can select Build New .
How do I set up a multipathed iSCSI Storage Domain?'
You can check the below RedHat Kbase for more detail. 
Does FCoE currently supported in RHEV 2.2? 
No, Actually, if you use hardware fcoe HBAs, then it can work
RHEV will just see the LUN's, without managing the storage connections, so it will assume it's just FC 
 How to move the SPM (Storage Pool Manager) from Non Responsive RHEV-H to other active RHEV-H in the RHEV Data Centre from RHEV Manager?

 If for some reason if you RHEV SPM host went non responsive and if you want to move the SPM role from that Host to New Host , then you can either Reboot the SPM node using Power Management Button Provided If you have Power Management enabled and configured on all the host in that cluster or else you can simply reboot the host manually
Then from the RHEV Manager UI , Right Click on the SPM Host and Select "Confirm Host has been Rebooted". Then after some seconds the SPM status will moved to other active nodes in that Data Center.
 Reference Link :

Is booting a RHEV-H host from FC SAN a supported configuration?

Install and boot from san are supported.  It's treated pretty much like a local disk so no issues with this. Check the below URL for complete Set of  detailed information.
 How to Check your Local SAS device is Supported in RHEV 2.2 ?

RHEV Supports any device that multipath recognizes

TO check your disk is multipathable run the below command and verify

dmsetup ls --target=multipath

So for SAS and the like, just create an FC domain and choose the relevant LUNs they will appear in the list while attaching new Storage Domain in RHEV  and attach to the relevant DC and Create Virtual Machines on top of it .

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