iscsi volume data loss on LUN deletion?

[TORGEIRARNOY]

Hi,

I would like to straighten up some things. Is it correct that the data on a block volume is lost when the attached LUN is lost?

I tried the following:

1. Mount iSCSI volume to an Linux Server, and placed some data.

2. Demounted and logged out of the LUN.

3. Took the LUN offline and deleted it.

4. Made a new LUN, attached it to the same Volume, and logged in from the linux server again.

5. No partitions found ..

How would i recover the data on the volume blocks? I guess the LUN manages the filesystem.

[RAVI_PALADUGU]

LUNs provide a file system, like Volumes provide a file system, the major difference is who controls the files system. With a LUN the storage system can't see the file system, all it sees is one big file.  the host mounts the file system via iSCSI/FCP/FCoE protocols and lays a file system down inside, the host then controls that file system.

When you share out a volume it looks like NTFS to a windows box, or it looks like a UNIX filesystem to a unix box but in the end its just WAFL in the volume. With a LUN its a bit different, you first make a volume and then you put a LUN in the volume, the volume has WAFL as the file system, the LUN looks like one big file in the volume. You then connect to the storage system using a SAN protocol, the big file we call a LUN is attached to the host via the SAN protocol and looks like a big hard drive, the host then formats the hard drive with NTFS or whatever File system the unix box is using.  That file system is actually NTFS, or whatever its inside the LUN, which is big file inside of a Volume, which has WAFL as its file system.

I don't believe you can recover volume blocks related to the LUN you have deleted.

Hope it helps!

Regards,

RK

[AGUMADAVALLI · Accepted solution]

If you have enabled the snapshots on the volume level and deleted the LUN accidentally or for test. You can restore them from snapshots.

Normally, a LUN acts like the dedicated disk and what ever operations like delete or format the drive, will result in loss of the data just like c:\ drive.

Instead if you completely unmount and delete the dedicated disk, LUN will be destroyed but you can still view the snapshots associated with it at volume level and you can restore them using the snapdrive or snaprestore utility.

Both the utilities require the license.

thank you

AK G

[ASHWINPAWARTESL]

Yes, that's absolutely right.

Going back to your original question - You can recover the data on the volume blocks from the snapshots. That is what snapshots are all about, fastest way to get your data back. You have a data on LUN (as long as you have a snapshot available in the volume), you can restore the LUN from the snapshot. If you have snapdrive installed, just take a snapshot (OS consistent), disconnect the disk, on the filer - offline & delete the LUN. Back to snapdrive console - Connect disk - select the volume - go to the snapshot you created in previous step, and connect to the LUN. You are back in business!

[RAVI_PALADUGU]

Yes, that is 100% true. If you have snapshots for the volume you can always restore from there. But I think this question is more oriented in the case if there are no snapshots available at volume level. Is that correct Arnoy?

[TORGEIRARNOY]

Thank you very much for the replys. This made very much sense.
We do have snapshotting, so i will try restore in that way then.

The reson i asked was because we are considering SnapMirroring our iSCSI volumes that are mounted as VMware datastores.
But if there was no option to restore the LUN in some way, that would have been pointless.

It seems like the LUN will be automaticly restored when you break a SnapMirrored volume then.

Thanks again,

Torgeir