Sun ZFS Storage Appliance: NDMP Backup Server encounters Tape IO Error during LTO-5 tape drive initial access, places drive in "Append Only Mode"

Asset ID:	1-72-1368914.1
Update Date:	2011-11-23
Keywords:

Solution Type Problem Resolution Sure

Solution 1368914.1 : Sun ZFS Storage Appliance: NDMP Backup Server encounters Tape IO Error during LTO-5 tape drive initial access, places drive in "Append Only Mode"

Applies to:

Sun ZFS Storage 7420 - Version: Not Applicable and later [Release: N/A and later ]
Information in this document applies to any platform.
ZFSSA
ak 2010.Q3.4 and before
NDMP
IBM Ultrium 5
Symantec NetBackup 7.1 and higher

Symptoms

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On a Sun ZFS Storage 7420, NBU backups using a direct attached IBM Ultrium 5 drive could fail, while backups via network are run successfully.

Tests writing to and reading from the drive with tar succeeds without problems.

When running the NBU backup we see following entries in /var/ak/logs/system.sys:

Sep 20 13:06:03 cluster.fs /usr/lib/ndmp/ndmpd[17702]: [ID 702911 daemon.error] Failed to open device /dev/rmt/0n: Device busy.
Sep 20 13:20:24 cluster.fs /usr/lib/ndmp/ndmpd[17702]: [ID 702911 daemon.error] Tape read error: I/O error.

In the ndmp debug logs on the 7420 we see (when the backup starts):

10/07 10:59:02 DEBUG: [26][common_tape_open:1271]:Adapter device opened: /dev/rmt/0n
10/07 10:59:02 DEBUG: [26][is_tape_unit_ready:2579]:Unit not ready
10/07 10:59:05 DEBUG: [26][is_tape_unit_ready:2579]:Unit not ready
10/07 10:59:08 DEBUG: [26][is_tape_unit_ready:2579]:Unit not ready
10/07 10:59:11 DEBUG: [26][is_tape_unit_ready:2587]:Unit didn't get ready

In the NBU bptm log we see:

12:59:55.228 [5404] <2> manage_drive_attributes: report_attr, fl1 0x00200049, fl2 0x00000000
12:59:55.228 [5404] <2> manage_drive_attributes: Media is protected with APPEND_ONLY

and when the backup session tries to write to tape:

13:00:28.740 [5404] <4> write_backup_position: allow overwrite scsi command failed
13:00:28.740 [5404] <16> write_backup_position: allow overwrite operation failed to media id 0242L5, drive index 3, address 43188870

Changes

SCSI Stream Commands (SSC-4) has introduced a new data protection feature for tape drives called "Append Only Mode".

This feature causes the drive to prevent the overwrite of data on a cartridge unless the writing application performs a pre-authorization for the overwrite.
Pre-authorization for overwrite is a done with a new SCSI command (Allow Overwrite) that informs the drive that the data block at the current location is going to be overwritten.
Any attempt to overwrite a data block without pre-authorization returns a write protect error.
IBM LTO-5 drives support this feature (even with LTO-4 media).
Once set, LTO-5 drives remain in append mode until power cycled.

Cause

The new feature introduced in NetBackup 7.1 can cause NDMP backup failures. The Append-Only Mode described in Symantec Tech Note TECH143890 causes the drive to prevent the overwrite of data on a cartridge unless the writing application performs a pre-authorization for the overwrite. This feature is supported on IBM LTO-5 drives with LTO-4 or LTO-5 media. The feature is enabled by default and does not normally cause any issues if all systems accessing the tape device are NetBackup 7.1 Media Servers.

Solution

The solution to this issue is:
1. Login on the NetBackup Master server

2. Create a file /usr/openv/netbackup/db/config/DISABLE_APPEND_MODE (or <install_path>\netbackup\db\config\DISABLE_APPEND_MODE on Windows)

# touch /usr/openv/netbackup/db/config/DISABLE_APPEND_MODE

3. Restart netbackup

4. Test backups

References

https://www.symantec.com/business/support/index?page=content&id=TECH143890
https://blog.lewan.com/category/symantec/

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