topic Re: Can't write to mounted snapshot? in StoreVirtual Storage

Can't write to mounted snapshot?

Paul Hutchings — Fri, 03 Feb 2012 11:37:21 GMT

I do scheduled application managed snapshots of Exchange.

I want to be able to copy an old .EDB file so today I assigned a snapshot to one of our servers, and mounted it.

Despite having read/write selected in the CMC Windows says it is unable to write to the volume?

I'm running SAN iQ 9.0 and the server is Windows 2008 R2. I'm not sure whether it's something SAN or Windows related - there isn't much in the Event Logs.

Re: Can't write to mounted snapshot?

oikjn — Sat, 04 Feb 2012 00:13:17 GMT

snapshots are like pictures. They are fixed and cannot be written to. What you need to do is use that snapshot in CMC and create a smart clone. You can then mound and write to/from the clone.

Re: Can't write to mounted snapshot?

Emilo — Sat, 04 Feb 2012 16:20:51 GMT

Mounting the snapshot on a host
You can add a server to the snapshot when it is created, or add the server later. For information about
creating and using servers, see Chapter 16 on page 257.
1. If it is not already added, add the server on which you want to mount the snapshot to the
management group.
2. Assign the snapshot to the server, and configure the snapshot for read/write access.
3. Configure server access to the snapshot
4. If you mount an application-managed snapshot as a volume, use diskpart.exe to change the
resulting volume's attributes.

When you have mounted the snapshot on a host, you can do the following:
• Recover individual files or folders and restore to an alternate location
• Use the data for creating backups

-----------------------------------------------------------

Making an application-managed snapshot available on a stand-alone server
Use this procedure to make an application-managed snapshot available on a stand-alone server (not
part of a Microsoft cluster).
1. Disconnect the iSCSI sessions.
2. Do one of the following (based on what you want to do with the application-managed snapshot):
• Convert temporary space.
• Create a SmartClone.
• Promote a remote volume to a primary volume using:
• Failover/Failback Volume Wizard and selecting the “Failover the Primary Volume to the
Selected Remote Volume Below” option.
• Edit Volume and changing a remote snapshot to a primary volume.
3. Connect the iSCSI sessions to the new target volume.
4. Launch Windows Logical Disk Manager.
5. Bring the disk online.
6. Open a Windows command line and run diskpart.exe.
7. List the disks that appear to this server by typing the command list disk.
8. Select the disk you are working with by typing select disk # (where # is the corresponding
number of the disk in the list).
9. Display the options set at the disk level by typing detail disk.
If the disk is listed as read-only, change it by typing att disk clear readonly.
10. Select the volume you are working with by typing select volume # (where # is the
corresponding number of the volume in the list).
11. Display the volume's attributes typing att vol.
The volume will show that it is hidden, read-only, and shadow copy.
12. Change these attributes by typing att vol clear readonly hidden shadowcopy.
13. Exit diskpart by typing exit.
14. Reboot the server.
15. Verify that the disk is available by launching Windows Logical Disk Manager.
You may need to assign a drive letter, but the disk should be online and available for use.
16. If the server is runningWindows 2008 or later and you promoted a remote application-managed
snapshot to a primary volume, start the HP StorageWorks P4000 SAN/iQ CLI and clear the VSS
volume flag by typing clearvssvolumeflags volumename=[drive_letter](where
[drive_letter] is the corresponding drive letter, such as G:).
17. Reboot the server.

Re: Can't write to mounted snapshot?

Paul Hutchings — Sat, 04 Feb 2012 17:11:26 GMT

Thanks both. It turned out to be this:

http://itstor.blogspot.com/2011/11/read-only-volume-attribute-clear-after.html

Which makes sense as I knew I was doing it correctly from the P4000/snapshot point of view.

Re: Can't write to mounted snapshot?

Emilo — Sat, 04 Feb 2012 17:17:27 GMT

So applicaton managed snapshots are treated differently then regular ones.

it was the 2nd part of my post.

Re: Can't write to mounted snapshot?

Paul Hutchings — Sat, 04 Feb 2012 17:51:04 GMT

Yeah, I didn't see that in any of the documentation that I could find though. I'm sure it's in there somewhere, it just stumped me at the time.