Mapping volume as read-write and read-only

[jeff2000]

Hello. Is it possible to map a Nimble volume as read-write to a group of hosts, yet read-only to another host? We are using FC, though I cannot imagine that would matter. Thank you. 

[Sheldon Smith]

I don't think anybody can do that. 

Once a volume is mounted read-write to a cluster of hosts, the clustering software reads and caches the file system. Another host mounting it (read-only) would find out what is there at that moment, also caching what it sees. It wouldn't have any way of knowing about continuing changes made to the file system by the cluster. Only by none of the systems caching the volume's file system would there be a possibility of seeing the volume's current contents. Lock the volume, read the file system, update a file, update the file system, unlock the volume.. All the systems would run at disk-write speeds, not at memory cache speeds. Performance would be abysmal. 

I think you would want to make a snapshot of the volume at some known consistent time, then present a clone of that snapshot to the host. Presumably you would periodically dismount the clone, get a new snapshot, and present a new close to the host only reading. In any event, the read-only host would not continuously see the updated contents of the volume.

What are you trying to accomplish?

[jeff2000]

Thank you for the reply, We currently run Dell Compellents and as you know they are EOL soon. They do have the capability to allow a host to mount a datastore as either read-write or read-only. We use this feature as we are a VMware shop and use Commvault backup with snapshots. So the Commvault media servers are physical windows servers backed by lots of SSD, that keep a backup local and send to cloud. As a level of precaution, we only let the Windows media servers mount all the array datastores as read-only, since they are only doing backups of the data. We have a couple of datastores it mounts read-write in order to restore, and we have never had an issue with windows hosing those datastores, ie suddenly writing a signature or whatver. But better safe than sorry.

[giladzzz]

Hi

Usually backup software mounts Vmware datastores as read only you

can see them in the disk administrator as off-line but the volumes can be

read write and the backup software knows how to deal with it

a better way is to use hardware storage integration and use storage snapshots

Regards

Give a KUDO if this helps

[Sheldon Smith]

Ahh. Looking through the HPE Nimble Storage documentation at https://infosight.hpe.com, search for CommVault. A search returns links to both GUI and CLI Admin Guides that mention using Volume Collections and CommVault.

Second, check with Commvault. I would expect they already have procedures for backing up HPE Nimble datastores.

With a VMFS datastore on HPE Nimble Storage, it would make sense to

1. Get VMs on the datastore(s) to a consistent state. Look at Nimble Volume Collections using vCenter application synchronization. VMtools are used to put the VMs into a consistent state, a Nimble (read-only) snapshot is made of the datastore and the VMs go back to normal.
2. Once you have the read-only snapshot, make a clone (a writable snapshot) from the read-only snapshot and present that to the Windows media server.
3. When the backup is complete, dismount the clone, delete the clone and optionally delete the snapshot.

Being snapshots, they are all isolated from the production datastore. And they are all thinly-provisioned, so they only need as much storage as necessary to preserve the data from the time of the snapshots while the backup is running.

[jeff2000]

Thank you. I think I will have us look into this solution. I appreciate your response.

[Cali]

A little remark Sheldon.

HPE MSA Storage and Datacore for example can do this.

It is useful if you have Backup Software and can not use Snapshot Backup.

In this case, we can save RO Mount the VMware Volumes to the Windows Backup Server for fast, LAN-Free Backup.
I've been asking for this for 3PAR/Primera Storage for years, may be easy to implement, but nobody is willing to do it.

It's more for smaller Environments, HPE thinks always Big.

Cali

[Sheldon Smith]

Cali, how does Windows not have a hissy-fit when presented with a RO volume?

[Cali]

No, it's best Practice.
Have to set "diskpart automount disable".
Example Veeam:
Veeam Backup & Replication Best Practices (learnvmware.online)
vSphere Proxy - Veeam Backup & Replication Best Practice Guide
Present LUNs as read-only to the backup proxy server. This capability is supported by most modern storage. When possible, implement read-only LUN masking on the storage system.
We do it with MSA.
The main problem is if only using "diskpart" and the Customer reinstall Windows without unmounting the Volumes first, Windows Setup corrupting all VMFS Datastores attached to that Windows Server.
Cali