Monthly Archives: September 2013

Restoring NetApp LUNs

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The other day, I was tasked to restore a NetApp LUN from several years ago. Since the backup was so long ago, I have to restore it from an archived tape. After restoring the file, it did not show up as a LUN. It turned out that there are few rules to follow in order to restore LUN from tape and that it shows up as LUN.

There are also a couple of requirements when backing up LUNs to tape. Thankfully when we backed up the LUNs, we followed these rules:

1. The data residing on the LUN should be in a quiesced state prior to backup so the file system caches are committed to disk.

2. The LUN must be backed up using a NDMP compliant backup application in order for it to retain the properties of a LUN. Symantec Netbackup is an NDMP compliant backup application.

When restoring, I learned that:

1. It must be restored to the root of a volume or qtree. If it is restored anywhere else, it will simply show up as a file and lose the metadata allowing it to be recognized as a LUN.

2. The backup software should not add an additional directory above the LUN when it is restored.

For instance, on Symantec Netbackup application, when restoring the LUN, you should select the option to “Restore everything to its original location.” If this is not possible, you can select the second option which is “Restore everyting to a different location, maintaining existing structure.” This means that you can restore it on a different volume.

For example, if the LUN resides in /vol/vol1/qtree1/lun1 and we chose to restore to /vol/vol2, the location where the LUN would be restored is /vol/vol2/qtree1/lun1 because it maintains the existing structure.

Do not select the third option which is “Restore individual directories and files to different locations” because the Netbackup software will add an extra directory beyond the qtree and the LUN will not show up as a LUN.

When restore is complete, a “lun show -v” output on the NetApp CLI will show the restored LUN on /vol/vol2 volume.

Deduplication and Disk-based Backup

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Disk-based backup has been around for a long time now.  I remember when I first deployed a Data Domain DD560 appliance eight years ago. I was impressed by its deduplication technology.  Data domain appliances are disk storage arrays used primarily for backup.  We used it as a disk backup destination for Symantec Netbackup via NFS.  Data Domain sets itself apart because of its deduplication technology.  For instance, in our environment, we are getting a total compression (reduction) of 20x; which means that our 124TB data only uses 6TB of space – a very large space savings indeed.

In addition, disk-based backup makes it very fast and easy to restore data. The need to find the tapes, retrieve them, and mount them have been eliminated.

In fact, the need for tapes can be totally eliminated.  A lot of companies are still using tapes to store them off site for disaster recovery.  If you have a remote office site, a Data Domain appliance can be replicated to your remote site (or disaster recovery site).  What is nice about Data Domain replication is that only the deduped data is sent over the wire.  This means less bandwidth consumption on your WAN (Wide Area Network).

Deduplication technology is getting better. Storage vendors and backup software vendors are offering it in different flavors.  With the cost of disk going down, there is really no need for tapes. Even long term retention and archiving of data can now be stored on a low cost, deduped disk storage array.