Recover from partial backups

The NBU is virtualy the same, same options ...  The main difference from memory is it frops the leading / so retores are relative to where you, not absolute (making althernate restore locations possible).

This is the posh way to do it  ...  It was aimed at images that span tapes, but works fine for a single tape.  You actually get the data off the tape with dd, then untar the files later.  

How to use dd to read data off a tape (Unix/ Linux)

On occassion it may be necessary to try and read data off a tape if there is a failure in NetBackup.  Usually this will be only to demonstrate that the tape is unreadable due to an issue outside of NetBackup.

It is easier to explain this via example.

We can see from bpimagelist that the image nbmedia00_1418641103 spans 2 tapes, E01001 and E01002

IMAGE nbmedia00 0 0 8 nbmedia00_1418641103 nbmedia_big 0 *NULL* root Full 0 1 1418641103 130 1419850703 0 0 2545152 1 1 2 0 nbmedia_big_1418641103_FULL.f *NULL* *NULL* 0 1 0 0 0 *NULL* 0 0 0 0 0 0 0 *NULL* 0 0 0 *NULL* 269 0 0 740 0 0 *NULL* *NULL* 0 0 0 0 *NULL* *NULL*
HISTO -1 -1 -1 -1 -1 -1 -1 -1 -1 -1
FRAG 1 1 1566208 0 2 6 1 E01001 nbmedia00 262144 2 1418641103 2 0 *NULL* 1419850703 0 65537 0 0 0 1 0 1418641233 0 *NULL* *NULL*
FRAG 1 2 978944 0 2 6 1 E01002 nbmedia00 262144 2 1418641103 2 0 *NULL* 0 0 0 0 0 0 1 0 0 0 *NULL* *NULL*

It does not actually matter if the image spans multiple tapes, or is contained on a single media, the procedure is exactly the same.

First, use scsi_command -map to obtain an image of what is on the tape, this needs to be done in fragment order, so E01001 is the first tape as it contains fragment 1, E01002 is the second tape as it contains fragement 2.

[root@nbmedia00 testdata]# scsi_command -map -f /dev/nst1
00000000: file 1: record 1: size 1024: NBU MEDIA header (E01001)
00000001: file 1: eof after 1 records: 1024 bytes
00000002: file 2: record 1: size 1024: NBU BACKUP header
          backup_id nbmedia00_1418641103: frag 1: file 1: copy 1
          expiration 1419850703: retention 1: block_size 262144
          flags 0x0: mpx_headers 0: resume_count 0: media E01001
00000003: file 2: record 2: size 262144
00006121: file 2: eof after 6119 records: 1603798016 bytes
eot

We see that the header for the backup image nbmedia00_1418641103 is located at file 2, and the data fragment is immediate after the header as expected.

We need to first read this fragment using dd, into a file on disk, followed by the actual data in fragment 1.

We can build the commands required by referencing the output of scsi_command -map output, consideration must be given to filenames and blocksize used to allow the read via dd to be successful, and correct identification of the files later.  In this example we have used the backupid, follwed by a description of what part of the image the file relates to.

NOTE:
We want to position the tape to file 2, fsf 1 is correct as it positions after file 1, which of course is just before file 2.
mkdir /tmp/recover

mt -f /dev/nst1 rewind
mt -f /dev/nst1 fsf 1
dd if=/dev/nst1 of=/tmp/recover/bu-nbmedia00_1418641103_frag1header bs=1k   count=1
dd if=/dev/nst1 of=/tmp/recover/bu-nbmedia00_1418641103_frag1 bs=256k

A quick look at the files created :

-rw-r--r-- 1 root root 1603796992 Dec 15 03:16 bu-nbmedia00_1418641103_frag1
-rw-r--r-- 1 root root       1024 Dec 15 03:15 bu-nbmedia00_1418641103_frag1header

The frag1header (which is the backup header) is 1K in size which is correct for a header.

We now need to recover any remaining fragments for the image from the next tape, so as before, we repeat the process and run scsi_command -map -d <device> on the next tape, E01002.

00000000: file 1: record 1: size 1024: NBU MEDIA header (E01002)
00000001: file 1: eof after 1 records: 1024 bytes
00000002: file 2: record 1: size 1024: NBU BACKUP header
          backup_id nbmedia00_1418641103: frag 2: file 1: copy 1
          expiration 1419850703: retention 1: block_size 262144
          flags 0x0: mpx_headers 0: resume_count 0: media E01002
00000003: file 2: record 2: size 262144
00003827: file 2: eof after 3825 records: 1002439680 bytes
00003828: file 3: record 1: size 1024: NBU EMPTY header (file 2)
00003829: file 3: eof after 1 records: 1024 bytes
eot

Here we see that we have frag 2 of backup header for frag 2 of image nbmedia00_1418641103 at the position file 2, so we can again put the required commands together.
In this case, because the fragements we want are both the first fragments on the tapes, the commands we need are the same, so we just change the filenames.

mt -f /dev/nst1 rewind
mt -f /dev/nst1 fsf 1
dd if=/dev/nst1 of=/tmp/recover/bu-nbmedia00_1418641103_frag2header bs=1k   count=1
dd if=/dev/nst1 of=/tmp/recover/bu-nbmedia00_1418641103_frag2 bs=256k

Looking now at the files we have created :

-rw-r--r-- 1 root root 1603796992 Dec 15 03:16 bu-nbmedia00_1418641103_frag1
-rw-r--r-- 1 root root       1024 Dec 15 03:15 bu-nbmedia00_1418641103_frag1header
-rw-r--r-- 1 root root 1002438656 Dec 15 03:22 bu-nbmedia00_1418641103_frag2
-rw-r--r-- 1 root root       1024 Dec 15 03:22 bu-nbmedia00_1418641103_frag2header

We have the two backup headers (one for each fragment) for reference if required, and the two files holding the actual data.

We can then 'cat' the two files containing each fragment of the image into one file:

cat bu-nbmedia00_1418641103_frag* >bu-backup

And read this single tar file back, which contains the data from the backup.

[root@nbmedia00 recover]# /usr/openv/netbackup/bin/tar tvf bu-backup
Erwxr-xr-x root/root 103 Dec 15 02:58 2014 .AtTrIbUtEs.0
--Extra header --
drwxr-xr-x root/root   0 Dec 15 02:41 2014 /
drwxr-xr-x root/root   0 Dec 15 02:49 2014 /testdata/
-rw-r--r-- root/root 1532471296 Dec 15 02:50 2014 /testdata/tarfile1