Monday, 26 October 2015

Adventures using Availability Groups and RBS with SharePoint 2013

The concept behind a remote blob storage is pretty simple, see this for instance. I just want to talk about the myriad issues we've had when using RBS. with availability groups.

Our database setup uses Availability Groups, which, and this is controversial, is a cheap cluster. I do get that there are advantages to availability groups but these seem to be outweighed by the disadvantages. I know this is just my opinion and that I also know nothing about availability groups, HA clusters or anything in general, thank you for pointing out.

So what are the drawbacks of AGs?

  • Official Support is patchy. e.g. in Dynamics CRM 2013 one is forced to update the database directly.
  • Performance can be an issue as the database is always using at least two boxes.
  • Stuff flat out refuses to work, e.g. RBS Maintainer, various SharePoint database related operations.
To the AG mix we introduced RBS and this is were things started to go horribly wrong for us.

The first issue we encountered was the inability to delete a content database from SharePoint, which is not a major issue but it's really annoying.

The second issue was that the RBS maintianer would not work, so the storage requirements would just keep growing. This might not be an issue if you don't plan to archive your documents, but our DB had ~500GB of docs, about 2/3 of which were old but for contractual reasons needed to be kept.

This effectively put a nail in the coffin of the RBS + AG combo but there is more.

In order to load the ~500 GB document, we had a tool to upload the documents to SharePoint. This tool was multi-threaded and it essentially read the documents from the source DB and uploaded them to SharePoint, using the SharePoint CSOM model.

At this point, it's worth mentioning that our hosting provider does not guarantee any sort of performance level, too long to explain.

A couple of weeks back, with RBS on the database, we did a trial run of the upload and we were hitting very poor rates, ~ 4 GB per hour.

Last week, after RBS had been disabled and the content databases recreated, we tried a second trial run and the speed jumped to ~ 20 GB per hour.

I can't say that our RBS configuration was perfect, I think the threshold was on the low side (128 KB) but even so, the speed increase has been massive.

It actually gets better, because the 4 GB per hour figure was using both servers in the farm, whereas the 20 GB per hour figure was simply using one.

yes, yes, I know our hosting provider is crap and 128 KB is below the recommendation, but a 5 fold increase in transfer rates and a lowering of the error rate to almost zero is something that should be considered.

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