Backing up cloud data (and the cost of mistakes)

Backups are useful for two major purposes: full recovery of everything lost in a hardware failure and partial recovery of something lost due to an user – or developer – error. Cloud providers have strong incentive to do everything to eliminate the first kind of problem, but I fear the second case more.

From what one can glean from the few published datacenter articles, cloud datacenters seem to deal with backup issues by continuously replicating the data into multiple storage devices so that data loss due to a hardware failure becomes sufficiently unlikely. This is understandable, as building a sufficiently big backup system would probably be quite costly indeed. But also, it means that there is only a single copy of the data. No snapshots of the past, just the current state – hopefully in pristine shape.

While having a single copy definitely saves storage space and reduces maintenance headaches, it also makes you very prone to data corruption. Say, you have a web application running in the cloud. A malicious hacker finds the cloud equivalent of a SQL Injection vulnerability and succeeds in messing up your production database. Well, it was replicated on all those servers, but by the time you realize something is wrong, all the copies contain beautifully synchronized corrupt copies of your data. At this point you start yearning for backups which you probably didn’t make.

Case: SharePoint Online

A colleague of mine found a blog post by Sander de Koning on BPOS backup strategies (for those of you who don’t know, BPOS is Microsoft’s online umbrella offering for SharePoint, Exchange et al.). The post brings up an interesting tidbit from the BPOS documentation on backups: SharePoint Online sites have practically zero protection against human error, particularly in a reasonably serious case of “SharePoint site deleted by mistake”.

While recovering from user-induced data loss not caught by the SharePoint recycle bin might require serious effort even with an on-premises installation, it is by and large possible given the availability of sufficiently frequent backups. The operation would probably involve building a separate SharePoint installation, restoring the databases onto it, finding the last valid snapshot of the destroyed piece of data and then merging it back into production via some sort of import/export. Not trivial, but on most installations, you could do it in a day.

When using SharePoint online, your options are pretty much limited. You’d probably end up searching for the latest copies of missing data by looking at the client computers last used for editing said data. Well, it’s a bold assumption to think you’d find recent copies on the local disks even if you knew where and what to look for – after all, centralizing data storage is pretty much what a cloud-based workgroup app is attempting to do! It goes without saying that using a cloud based office suite á la the forthcoming Office 2010 offering or Google Apps would exacerbate the problem further.

This is not meant to bash BPOS or SharePoint Online – the backup problem alone doesn’t make a good service bad. Yet still, it’s a worthy consideration for truly critical data. Cloud is all about trust, but this time trusting Microsoft isn’t enough. You should also be able to trust your users, which may require some pretty demanding discussions and compromises.

What could we do?

As the example above indicates, there is room for improvement of data storage safety in the cloud. That said, how could we mitigate the risks for cloud applications in general?

One could snapshot the data onto a local server and store it securely somewhere. That’s definitely a good option, although the available methods of sufficiently fast bulk import/export seem rather limited at this time. The throughput of most standard data transfer APIs – if they even exist! – would hardly be enough for a nightly snapshot of a large business application database. Amazon offers a physical import/export mechanism based on portable storage devices, but that’s far from being fast enough for backup purposes. Also, if you’re offloading storage to the cloud because of the costs involved in maintaining sufficient local capacity, this may not be such a good idea.

Even if you don’t have too much data, getting a really good snapshot may not be trivial due to the slowness of data transfer and the eventually consistent nature of cloud databases. At any rate, to get a useful backup for most purposes, you’d need to write the backup application yourself until something generic gets published.

Another way to approach this would be to improve the resilience of the logical data structure itself. In-database versioning, recycle bins and similar features could add restorability not just to the system administration level, but into the normal user interface as well. This would give decent protection against user errors, but might or might not protect against malicious attacks. Certainly it would provide no protection against most data-corrupting code mistakes, which would have to be ironed out in testing environments. Also, the complexity involved in implementing data versioning would probably contribute to the amount of data loss bugs, particularly as developers with cloud database skills are still very scarce.

There are talks about getting backup set functionality into SQL Data Services, but nothing has been announced as far as I know.

So what can we do? Develop with due diligence, possibly create local snapshots with custom apps, and secure the most critical pieces of data by in-database versioning. Those are decent options for custom cloud software. For the readily available cloud services such as BPOS, it’s far more about finding out your real needs and the pushing your service provider to meet your needs.

And if you want to put all this into a real life perspective with some drama involved, get yourself acquainted with the ma.gnolia story.

June 5, 2009 · Jouni Heikniemi · 3 Comments
Tags: ,  · Posted in: Cloud, Windows IT

3 Responses

  1. ambreen tariq - November 14, 2009

    the deeper the knowledge of cloud computing horrifies there are chances that one can hack your cloud

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