Backup to a VTL fails with a 'Write Data invalid block size 65536 expected 32768' error. (4037035)

Backup to a VTL fails with a 'Write Data invalid block size 65536 expected 32768' error.

The following messages and errors would appear within the NetVault logs:

1] Job Message   2014/12/07 18:00:01   214   Jobs   DCDR02   Starting job 214 'WPEPOSSQL OLAP (Full)' (Phase 1 , Instance 25) for UID 6
2] Job Message   2014/12/08 20:49:29   214   Media   DCDR02   (DCDR02: E:\VTL\VTL01) Media in 'DRIVE 1:DCDR02' assigned to job ready for data transfer
3] Background   2014/12/08 20:49:29   214   Media   DCDR02   Sent Plugin space left estimate of 92881 Mb
4] Error   2014/12/08 20:49:49   214   Media   DCDR02   DCDR02 E:\VTL\VTL01\drives\1: had media error

With sub text:
This will almost certainly be a hardware error either with the SCSI card. The problem is probably not due to drive order as there is no message that the library cannot move a tape to/from a slot. Contact the hardware supplier as this will be a problem with the drive or library.

DEVDISK :00692   80       3 204949 Write Data invalid block size 65536 expected 32768
MEDWRITE:00692  186       1 204949 Device write data out: UNKNOWN (262)

5] Error   2014/12/08 20:49:49   214   Media   DCDR02   Hardware error transferring data (writing) to Mid 'DCDR02 06 Sep 22:01-1', marked read only

With sub text:
DEVMGR  :00692  273       0 204949 bHardwareError = TRUE

6] Error   2014/12/09 11:22:38   214   Data Plugin   DCDR02   Error while closing the backup stream
7] Error   2014/12/09 11:22:41   214   Jobs   DCDR02   Job Status: Backup Failed

All the VTL drives Media Block Size (MBS) were changed from 32 to 64 to increase the backup performance, but the VTL media were not blanked.
Therefore the following error as above “Write Data invalid block size 65536 expected 32768” would be expected.

You need to blank the media in order that the new MBS will take effect (it is only possible to have one MBS on any one media).
When you blank your media, the data will be lost.
So if you still need the data, then perform a Data Copy of all the backups that reside on the VTL to another device i.e. a tape library, another VTL that resides on a different hard drive to the current VTL, SmartDisk or a DR4X00/6000. Further information is in Chapter 17 of the NVBU Administrators Guide on the following link:

https://support.quest.com/netvault-backup/technical-documents

If you can’t blank the media, then you can change the MBS back to 32 again and the error will disappear.

Additionally when NetVault has problems writing to tape or VTL, it marks it as "Read Only". This is for your benefit and prevents you finding out at a later date that the Backup didn't work when you wish to perform a Restore.
These error messages are supplied from the library to NetVault i.e. these are not NetVault error messages.
These errors generally point to the following reasons for a VTL:

A] Read / Write Heads within the hard drive are faulty.
B] Hard drive and / or other hard drive hardware / firmware are damaged.

So if there are still “Read only” errors after the MBS was changed back to 32 and/or on MBS 64 and blanking the media; then there is a problem with the hard drive and can try and fix the bad sectors or the hard drive may need replacing.
I would advise to perform the following steps to re-create your VTL:

1] Perform a Data Copy of all the backups that reside on the VTL to another media i.e. a tape library, SmartDisk or DR4X00/6000. Further information is in Chapter 17 of the NVBU Administrators Guide on the following link:

https://support.quest.com/netvault-backup/technical-documents

2] Make a screenshot of the NVBU Device Management - VTL name and configuration settings, so that you can re-create a new VTL with the same name (so the backup target set won’t change) and same settings.
3] Blank all the VTL media from the faulty VTL, otherwise when you re-create your VTL, the old and new VTL media will be added together and you’ll exceed your license.
4] Remove the old VTL from NVBU Device Management.
5] Delete the old VTL folders on the drive.
6] Run the following command to check and fix any bad problems with the hard drive. For example: “chkdsk /f D:”
7] Re-create the VTL in NVBU Device Management with the same name and configuration settings made in step two.
8] Perform some test backups.