Basics – Understanding NetWorker Dependency Tracking

 Backup theory, NetWorker  Comments Off on Basics – Understanding NetWorker Dependency Tracking
Sep 162017

Dependency tracking is an absolutely essential feature within a backup product. It’s there to ensure you can recover data through the entire specified retention period for your backups, regardless of what mix of full, differential and/or incremental backups you do. It’s staggering to think there are some backup products out there (*cough* net *cough* ‘backup’), that treat backup retention with such contempt that they don’t bother to enforce dependency preservation.

Without dependency tracking, you’ve always got the risk that a recovery you want to do on the edge of your specified retention period might fail.

NetWorker does dependency tracking by default. In fact, it only does dependency tracking. To understand how dependency tracking works, and what that means for protecting your backups, check out my video below. (Make sure to switch it into High Definition – it’s not about being able to see more of my beard, but it is to make sure you can see all the screen content!)

Dependency tracking is such an important feature in data protection that you’ll find it’s also covered in my book, Data Protection: Ensuring Data Availability.

On another note, I’m starting a new project. I may work in IT, but I’ve always been a fan of philosophy, too. The new project is called Fools Rush In, and it’s going to be an ongoing weekly exploration of topics relating to ethics in IT and modern technology. It’s going to be long-form in its approach – the perfect thing to sit down and read over a cup of coffee or tea. This’ll be an exciting journey, and I’d love it if you joined me on it. The introductory article is …where angels fear to tread, and the latest post, What is Ethics? gives a bit of a primer on schools of ethical thought and how we can start approaching ethics in IT/technology.

Jan 082010

I thought it about time that I cited the two key reasons why, if faced with a choice between NetWorker and NetBackup, I would choose NetWorker every time.

As you might expect, given my focus on backup as insurance, both of these reasons are firmly focused on recovery. In fact, so much so that I still don’t really understand why EMC doesn’t go to market with these points time and time and time again and just smack Symantec around until it’s blue in the face and begging for mercy.

Reason 1: NetBackup does not implement backup dependencies

I struggle to call NetBackup an “enterprise” backup product because of this simple fact. Honestly, backup dependencies are critically important when it comes to guaranteeing anything but last-backup recoverability.

What does this mean?

In short, as soon as a backup hits its retention period in NetBackup, it’s toast – it’s a goner.

Irrespective of whether there are any backups of the same filesystem/data set that requires the “outside retention” backup for recovery purposes.

I can’t sum this up any other way: in a backup product, I see this as recklessly irresponsible. It provides a focus on media savings that even the most miserly bean cruncher would admire. Well, until the bean cruncher’s system can’t be recovered from 6 weeks ago to fulfil audit requirements.

Reason 2: True Image Recovery is “optional”

If you’ve grown up in a NetWorker world, where the emphasis has always been, and will always continue to be on recovery, this will, like the reason above, make you soil yourself. Imagine having a full backup plus six incremental backups of a directory, and wanting to recover the filesystem from last night. Now imagine just selecting the full plus the incrementals for recovery and getting back everything generated during that time.

Even the files that had been deleted between backups. I.e., you don’t get back what the filesystem looked like at the time of the backup that you’re recovering from, but what it looked like for every backup that you’re recovering from.

NetWorker, once, in the 5.5.x stream implemented this. It was called a BUG. In NetBackup, it’s a “feature”. In order to enable a correct recovery, you have to turn on “true image recovery”, something that takes extra resources, and is typically advised  that you keep the data just for a small cycle (e.g., 7 days) rather than the complete retention time for the backups.

There’s another word for this: Joke.

On another front…

As recently as December I mentioned that I wished EMC would get their act together and implement inline cloning – one of the few things where I saw that NetBackup had a distinct competitive advantage over NetWorker.

Maybe it was the glow of the cider, but I had an epiphany in Copacabana on a hill watching (probably illegal) fireworks in Avoca and Terrigal on new years eve. Inline cloning is no longer a compelling factor in a backup product. Why? Media streaming speeds have reached a point where companies with serious amounts of data just should not be implementing direct-to-tape backup solutions any more. Inline cloning was developed at a time when you’d want to generate both sets of tapes as quickly as possible, but only companies with very small data sets will find themselves not backing up to some disk unit first (be it say, ADV_FILE, or VTL, in NetWorker), and those companies won’t be constrained on backup/clone windows to a point where they’d need inline cloning anyway.

When not backing up direct-to-tape, there are several factors that mitigate the need to do inline cloning. In organisations with a very strong need for offsiting, there’s replication at a VTL or disk backup unit layer. In organisations that just need a second copy generated “as soon as possible”, doing disk/virtual tape to physical tape cloning following the backup should be fast enough to handle the cloning at appropriate performance levels.

In other words: there’s no need for EMC to implement inline cloning. As a technology, it’s a dead-end from a tape-only time. I feel somewhat silly this didn’t occur to me sooner.

The top 10 for 2009

 Architecture, Basics, NetWorker, Quibbles, Site, Support  Comments Off on The top 10 for 2009
Jan 062010

Looking at the stats both for this new site and the previous site, I’ve compiled a list of the top 10 read articles on The NetWorker Blog for 2009. The top 3 of course match the three articles that routinely turn out to be the most popular on any given month, which speaks something of their relevance to the average NetWorker administrator.

(Note: I’ve excluded non-article pages from the top 10.)

Number 10 – Instantiating Savesets

The very first article on the blog, Instantiating Savesets detailed the importance of distinguishing between all instances of a saveset and a specific instance of a saveset.

This distinction between using just the saveset ID, and using a saveset ID/clone ID combination becomes particularly important when staging from disk backup units. If clones exist and you stage using just the saveset ID, when NetWorker cleans up at the end of the staging operation it will remove reference to the clones as well as deleting the original from the disk backup unit. (Something you really don’t want to have happen.)

Recommendation to EMC: Perhaps it would be worthwhile requiring a “-y” argument to nsrstage if staging savesets from disk backup units and specifying only the saveset ID.

Recommendation to NetWorker administrators: Always be careful when staging that you specify both the saveset and the clone ID.

Number 9 – Basics – Important mminfo fields

In May I wrote about a few key mminfo fields – notably:

  • savetime
  • sscreate
  • ssinsert
  • sscomp
  • ssaccess

Sadly, I didn’t get the result I wanted with EMC on ssaccess. Documented as being updated whenever a saveset fragment is accessed for backup and recovery, the most I could get was an acknowledgement that it was currently broken and to lodge an RFE to get it fixed. (The alternative was to have the documentation changed to take out reference to read operations – something I didn’t want to have happen!)

Recommendation to EMC: ssaccess would be a particularly useful mminfo field, particularly when analysing recovery statistics for NetWorker. Please fix it.

Number 8 – Basics – Listing files in a backup

Want to know what files were backed up as part of the creation of a saveset? If you do, you’re not unique – this has remained a very popular article since it was written in January.

Recommendation to EMC: This information can be retrieved via a combination of mminfo/nsrinfo, but it would be handy if NMC supported drilling down into a saveset to provide a file listing.

Number 7 – Using yum to install NetWorker on Linux

NetWorker’s need for dependency resolution on Linux for installation of the client packages in particular drew a lot of people to this article.

Number 6 – Basics – mminfo, savetime, and greater than/less than

This article explained why NetWorker uses the greater than and less than signs in mminfo in a way that newcomers to the product might find backwards. If you’re not aware of why mminfo works the way it does for specifying savetimes, you should be.

Number 5 – 7.5(.1) changed behaviour – deleting savesets from adv_file devices

This was a particularly unpleasant bug introduced into NetWorker 7.5, thankfully resolved now in the cumulative service releases and NetWorker 7.6

The gist of it is that in NetWorker 7.5/7.5.1 (aka 7.5 SP1), if you deleted a saveset on a disk backup unit, NetWorker would suffer a serious failure where it would from that point have issues cleaning regular expired savesets from the disk backup unit and insist that the disk backup unit had major issues. The primary error would manifest as:

nsrd adv_file warning: Failed to fetch the saveset(ss_t) structure for ssid 1890993582

This was fixed in, thankfully.

Recommendation to EMC: Never let this bug see the light of day again, please. (So far you’re doing an excellent job, by the way.)

Number 4 – NetWorker 7.5.1 Released

I’ve recently noticed a disturbing trend among many vendors, EMC included, where once a new release is made of a product, sales and account staff become overly enthusiastic about recommending new releases. This comes on top of not really having any technical expertise. (Please be patient, I’m trying to put this as diplomatically as possible.)

One of the worst instances I’ve seen of this in the last few years was the near-hysterical pumping of 7.5 thanks to some useful features to do with virtualisation in particular. I’ll admit that my articles on the integration between Oracle Module 5 and NetWorker 7.5, as well as Probe Based Backups may have added to this. However, there was somewhat of a stampede to 7.5 when it came out, and consequently, when it had some issues, there was strong enthusiasm for the release of 7.5.1.

This is why, by the way, that IDATA maintains for its support customers a recommended versions list that is not automatically updated when new versions of products come out.

Recommendation to EMC: Remind your sales staff that existing users already have the product, and not to just go blindly convincing them to upgrade. Otherwise you’ll eventually start sounding like this.

Number 3 – Carry a jukebox with you (if you’re using Linux)

During 2009, Mark Harvey’s LinuxVTL project first got the open source LinuxVTL working with NetWorker in a single drive configuration, then eventually, in multi-drive configurations. (Mark assures me, by the way, that patches are coming real soon to allow multiple robots on the same storage node/server.)

Lesson for me: With the LinuxVTL configured on multiple lab servers in my environment, I’ve really taken to VTLs this year, and considerably changed my attitude on using them. (I’ll say again: I still resent that they’re needed, but I now respect them a lot more than I previously did.)

Lesson for others: Even Mark himself says that the open source VTL shouldn’t be used for production backups. Don’t be cheap with your backup system, this is an excellent tool for lab setups, training, diagnostics, etc., but it is not a replacement to a production-ready VTL system. If you want a VTL, buy a VTL.

Number 2 – Basics – Parallelism in NetWorker

Some would say that the high popularity of an article about parallelism in NetWorker indicates that it’s not sufficiently documented.

I’m not entirely convinced that’s the case. But it does go to show that it’s an important topic when it comes to performance tuning, and summary articles about how the various types of parallelism interact are obviously popular.

Lesson for everyone: Now that the performance tuning guide has been updated and made more relevant in NetWorker 7.6, I’d recommend people wanting an official overview of some of the parallelism options checking that out in addition to the article above.

Number 1 – Basics – Fixing “NSR peer information” errors

Goodness this was a popular article in 2009 – detailing how to fix the “NSR peer information” errors that can come up from time to time in the NetWorker logs. If you’re not familiar with this error yet, it’s likely you will eventually as a NetWorker administrator see an error such as:

39078 02/02/2009 09:45:13 PM  0 0 2 1152952640 5095 0 nox nsrexecd SYSTEM error: There is already a machine using the name: “faero”. Either choose a different name for your machine, or delete the “NSR peer information” entry for “faero” on host: “nox”

Recommendation for EMC: Users shouldn’t really need to be Googling for a solution to this problem. Let’s see an update to NetWorker Management Console where these errors/warnings are reported in the monitoring log, with the administrator being able to right click on them and choose to clear the peer information after confirming that they’re confident no nefarious activity is happening.

Wrapping Up

I have to say, it was a fantastically satisfying year writing the blog, and I’m looking forward to seeing what 2010 brings in terms of most useful articles.

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