backup vxfs (veritas-) filesystems

[Kay Liesenfeld]

Hi,

Veritas support is unfortunalety not able to answer this simple question, so maybe one of the other HP users can help me with that case:

I'm using Veritas vxfs filesystem and my backup strategy is to TAR everything every night to tape. At night, normally no (or not much) data will be changed.

Do I have to use snapshots or is it possible to backup the "life" filesystem?

Sure, I AM ABLE tar any file, but will I be able to use that files in case of restore?

Thanks in advance.

Kay.

[Michael Tully]

Hi Kay,

I wouldn't use 'tar'. You should perhaps look into using 'fbackup'. It has it's own in built mechanism so that you can utilise incremental backups, which can easily be restored. Have a look in 'sam' it is all there.

You if wanted to go out and spend some money you may to look at omniback, legato etc.

Michael

[steven Burgess_2]

Hi Kay

Yes - you will be able to use your 'tar' backups to restore files , but you won't be able to recover a system from your tar backups

What do you class as the 'life' filesystem ?

As a backup strategy I would use ignite to backup your vg00 - Then, if you for whatever reason lose your system to disk failure etc , you will be able to restore it

A much prefered backup solution for HP systems is fbackup. This is more flexible across the HP platform in the fact that it is easy to backup and restore over the network. You also don't have to mess around when you want to recover files to other areas. You can backup files over 2 gig and you can verify the backup to confirm that the data on the tape is as is written on the index. You also have the incremental feature . The only problem with fbackup is that you can't restore a file to another OS - ie Solaris

HTH

Steve

[Stefan Farrelly]

If you use tar (and you can use it) then all your applications need to be shutdown in order to ensure file integrity.

OR

use JFS snapshots to create a snapshot of your live filesytsems, mount the snapshots then you can tar them to backup and you will have file system integrity. Nice and safe.

[Kay Liesenfeld]

Thank you all,

if using fbackup or "SAM Automated Backup" feature, there is no need to perform a snaphot of the filesystems which I want to backup?

And I'll have consistant data on the tape?

One more question: there is an Oracle database to backup, in this case, I have to switch the database in Online Backup mode. This is not possible when using SAM automated backup.

One chance will be fbackup, I'll check this. But on the other hand, TAR is a nice feature, so why don't using it?

The question is, if a snapshot is a must-do or only one possibility to get more comfort.

[Kay Liesenfeld]

Steven,

thanks again for this answer.

Now the only open question is the one concerning file system integrity.

Do have to make a snapshot before invoking the backup or is it just a feature to get a filesystem as it was in one second?

Are backupped files without a snapshot physically consistent and just logically not?

Or is a snapshot a must-have before any backup (however I decide to do it), otherwise I will get corrupt files back in case of restore?

(Of course, all system files are on HFS, so they don't matter.)

[steven Burgess_2]

Kay

Could you please expand on your word 'snap shot'

If you talking about lvm configuration then in your backup script you can specify vgcfgbackup

man vgcfgbackup

for exact options

If for some reason you lose for lvm configuration you use vgcfgrestore

man vgcfgrestore

for exact options

If you mean a 'snap shot' as an ignite then I would say it's safe to run one once a month. Some may disagree and advise weekly

As far as the size of your filesystems across all areas - keeping this so you know that you have a copy of whats on the system - plus other configuration. There is a command that is part of the ignite package called print_manifest.

As far as the consistency of a backed up file. The file will be as good a state as it was when backed up. I wouldn't worry to much about that.

To see what has actually been backed up

Have your tape loaded

frecover -I /tmp/tapeindex

This will create an index of files that fbackup believes has been copied to tape

fbackup backs up your system in alphabetical order, ie your last filesystem will be /var

You can ensure that you have a complete backup
by looking at your index (as above)then attempt to restore the last file on the tape

frecover -x -v -f /dev/rmt/0m -i /var/

Hope this helps

PAP

Steve

[steven Burgess_2]

Kay

Have we answered all your questions ?

Regards

Steve

ps

PAP

[Carsten Krege · Accepted solution]

Hi Kay,

no, the snapshot of a VxFS filesystem doesn't necessarily guarantee the consistency of your backup. It solely guarantees that the snapshot filesystem doesn't change during the time you have it mounted.

To understand how it works:

You create a snapshot filesystem with the "mount -F vxfs -snapof=... " command and from this time on all blocks that are going to be changed in the original filesystem are copied to the snapshot filesystem before, i.e. the original filesystem has all the new changes and the snapshot contains all the old blocks.

When you umount the snapshot, all the old blocks are simply removed, as the changes already went in the original filesystem.

You see that you really get a snapshot of your filesystem from the time when you issued the mount command.

However, this doesn't guarantee that your files are consistent internally. If you created a snapshot when an application was just modifying a file, you cannot expect the backuped file to be consistent from an application point of view (since you really backup a file that was currently modified).

To guarantee this consistency of a file from an application point of view, you would have to make sure that no files in the filesystem are kept open by an application, i.e. stop all applications gracefully that keep files open in this FS.

Database applications (Oracle, Informix,.. ) provide special online backup mechanisms that allow to do consistent backups while the application is running, but most other applications do not have such a feature.

fbackup is in some way smarter than tar. It tries to lock the file that is being backuped so that no other application can modify the file when fbackup accesses it.

As an alternative to snapshots many customers use MirrorDisk/UX' feature to lvsplit their LVM logical volumes, running fsck on the new lvol (to make the FS consistent again), mount it and backup the data. This is very much the same functionality as a vxfs snapshot filesystem can provide:

- No changes done during the backup,
- internal consistency of files from an application point of view only when no files were kept open during lvsplit

The disadvantages of using lvsplit are

- no protection of data during backup if not 2 mirror copies are used
- filesystem inconsistencies after lvsplit that need to be fixed with fsck
- user errors possible when using the wrong order of lvols with lvmerge command when the mirror is reestablished

Carsten

[Kay Liesenfeld]

Carsten,

ok, in this minutes I got an answer from Veritas too.

If there is no traffic on the file system, I don't need a snapshot to do a backup. It's only a good advantage when there's a lot IO during backup time.

You are right, I don't get any logical data consistence, but I get physical consistence even without a snapshot.

For my needs it's enough to turn Oracle in backup mode, TAR any files and remove Backup mode. I don't need a snapshot additionally.

However, thank you all, and Steven for your backup ideas. I will check that out!

Best regards,
Kay.