Saturday, 13 September 2014

The Perils of Beta Testing

Regular viewers will be aware that I've been using beta versions of unRAID 6 to run multiple virtual machines on MediaServer8.

I haven't been cursing edge with the betas, mainly due to time constraints, plus I was stuck on beta5 for a while as there as a kernel issue in beta 6 that prevented it from recognising my Marvell motherboard SATA controlllers.

However, I have been updating regularly and most recently installed beta 7. This allowed me install BtrFS on my cache and install multiple drives to cache as well. Indeed I'd done this to play around with Docker which up to beta 7 required BtrFS. Frustratingly, this requirement was removed in Beta8 so my time was somewhat wasted setting that up, or so I thought.

This week a really really nasty bug came to light affecting both unRAID beta versions 7 and 8. Any read or write activity to ReiserFS formatted drives could result in file corruption on those drives.

For a NAS system whose raison d'ĂȘtre is data storage, this is a pretty serious issue!

Not only could the files in question be affected, but it was thought other files on the drive could also become corrupted. The issue was file truncation but in an invisible way that was particularly difficult to detect.

To make matter worse, a lot of users running the beta had been busily copying data off ReiserFS disks in their arrays in order to convert them of alternative file systems newly available in the betas. Not good.

The guys at LimeTech were very proactive on the issue, announcing it when it became know, keeping people up to date via the forums and working flat out to produce a fix!

In my own case, I think I was lucky. Most of my day to ay activity is on my cache drive where my VMs live. These had been converted to BrtFS so were infected by the issue. I have very little read/write to the array proper which is still ReiserFS formatted. Time will tell, of course, but I think I'm ok.

This morning I updated to beta9 without issue.

It's a cautionary tale and has chastened me - I'll be a little more cautious in future!

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