An Innovative way to backup to tapes

Disk to Disk backups have become popular these days but if we exclude some exceptions, tapes are still the norm when it comes to long time retention and that is what we are going to talk about here. So here is a blog post on Tapes for a change.

How many times have you been in a situation to restore a backup that was more than a few months old and you could only restore the monthly backup? A request to restore a version of data that is more than a few months old is rare but when it comes, it is important and some times could have financial implications attached to it.

So, what if someone asked for data from say 17th Jan 2012? If one is not retaining daily backups for a long time, there is no way to restore that day’s backup. The best one can do is either weekly or monthly.

In this post I am going to talk about an innovative way to backup the data on your NetApp Storage using a technology called SMTape or SnapMirror to Tape.

SnapMirror, as some of you would know is the NetApp technology to replicate data to a Secondary site on Systems running Data ONTAP. Since SnapMirror integrates with Snapshot copies, one of the cool things about it is that it takes all the Snapshot Copies on primary with it to the DR site. So if one has created 100 Snapshot copies on a volume at primary, all the 100 Snaps will also be available on its replica at the DR site. This has multiple advantages like protection of data against corruption on primary spreading to the DR site, freeing up resources on primary by moving any tape based backups to the DR site, using Snapshot copies and clones for things like Reporting, Test & Dev etc. The other cool thing about SnapMirror is that it is deduplication aware, so only unique data is sent to the the DR site.

SMTape is an enhanced version of SM2T and replaces it starting Data ONTAP 8.0. SM2T started as a method to help seed DR sites using tape (another unique thing about SnapMirror) but it quickly became popular as a backup technique with NetApp customers especially in high file count environments. Since SM2T and now SMTape is a block based backup, it can increase the performance of small files backup by 2-10 times when compared to file based backups. As you can guess, it is a DR copy of one’s data on a tape. As is the case with SnapMirror, it takes all the Snapshot copies with it to the tape and sends only unique data as it is deduplication aware.

So consider a customer who is taking hourly, daily and weekly Snapshot copies on the NetApp Primary storage with retention period of a day, 30 days and 6 weeks respectively. If he opts to take a standard file based backup to tape, his weekly and monthly backups would only have data from that day. Alternatively if he opts to take a SMTape based backup, his weekly and monthly would not only have pre-deduplicated data from that day but also all the Snapshot copies on the volume being backed up. So in this example, a monthly SMTape backup will have a pre-deduplicated backup from the day and 60 Snapshot copies. Each of these Snapshot copies are a full backup but since the Snapshot copies are only block level incrementals, it would not mean 60 times the volume size. It would mean one full + changed data captured in the Snapshot copies. So if one had to restore the backup from 17th Jan 2012, it would mean restoring the backup from 30th Jan and then using the Snapshot taken on the 17th Jan 2012 for restoring the whole volume (instantaneously) or just a file.

This is something that is practically impossible with traditional file based backup as one would have to take a daily full backup everyday and store it. This would mean 365 tapes in a year if one’s data was to fit in a tape as compared to perhaps less than 15 with SMTape. The good thing about SMTape is that almost all major backup software vendors ((Symantec, Commvault, CA, EMC, Quest, Syncsort, HP, IBM etc.) support SMTape and in most cases it works on top of a NDMP license. There is no additional requirement to use it.

But as they say there is no such thing as a free lunch. SMTape has its limitations. One of them that I wanted to cover is that since it is an image level backup, one can’t do a single file recovery directly from the backup. But if you think about it with Snapshot copies and SnapMIrror/SnapVault in place, one has to go to the tape is if there is a disaster, in which case the whole volume has to be recovered or when there is a request for a file that is not on one of the Snapshot copies on the storage. And for such cases one should be OK to restore the whole volume to find the file from a particular day.

Below is a short comparison that I have created between SMTape and Standard Tape Backup.

Standard Backup and SMTape ComparisonThe above table should give you a good idea about SMTape and should make it easy to choose between the Standard Tape Backup and SMTape or use a combination of both.

For further details on SMTape, NetApp customers and partners can refer the Data Protection Tape Backup & Recovery Guide on the NetApp support site. Here is a publicly available TR that covers SMTape and Netbackup. For details on various other backup software, you can refer the Administration guides of the Backup software

Feel free to use the comments section to ask any question that you may have around SMTape and I’ll do my best to respond.


Satinder (@storarch)

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