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VhyVenom

Remotely modifying file - Does Read striping cause a scary mismatch? eg encrypted VHD/Truecrypt volume

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Hi,

 

So read striping is wicked for reads. It looks like it will pull from multiple disks when transfering. Sounds great to me!

 

But now the question: What happens when a remote volume or file is modified is saved? For example a mounted VHD or Truecrypt volume mounted remotely, modified, unmounted/committed. The saving/commiting doesnt write the whole volume back - it only writes the modified blocks. How does it know where to store the modifications back to?

 

Does DrivePool write modified blocks back at the same time to all copies?

 

I feel this is basic file system functionality 101 and ofcourse DrivePool does this - its late and its possible im not be thinking straight but a second confirmation would be helpful

 

thanks,

~v

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6 answers to this question

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If Real-Time duplication is enabled (and it is by default), then any write that occurs, is written to both disks at the same time.

You may want to check out this link:

http://stablebit.com/Support/DrivePool/2.X/Manual?Section=Performance%20Options

 

In fact, I believe that Alex (the developer) runs VMware VMs from DrivePool. And we have a few people that run HyperV VMs from the Pool as well.

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I run VMWare / Virtualbox and have run Hyper-V on and off from the pool. I test and develop DrivePool on the pool.

 

There have been issues in the past that were causing problems with virtualization products, but those have since been resolved. The latest 2.1 builds work beautifully for me.

 

For writes there is no "read striping", writes go to all the disks at the same time (I think you may be getting confused between reads / writes).

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Awesome. I appreciate the responses.

 

One last question on this line of thinking: Delayed Duplication is ONLY for new files? I couldnt imagine seeing modifications being tossed onto a feeder disk and then sent out to the disks at a later point if you enabled delayed duplication. Hope that makes sense.

 

Thanks,

~v

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I'm not sure what you mean by "delayed duplication" here.

 

Just to clarify, if "real-time duplication" is enabled (and it is by default), then any writes that occur are done to all of the files in the "set" simultaneously. Meaning that all files that are duplicated are kept in sync. 

 

Also, Duplication isn't responsible for pushing files off of a feeder disk. That's Balancing, and an entirely different subsystem from Duplication. While the two do interact, they have very different roles and do different things.

 

However, StableBit DrivePool does check periodically to make sure that the pool is properly duplicated, and will duplicate files as need, and flag any problem files for user resolution.

And duplication does use the balancer rules to determine where it should place files.

 

 

If you've disabled real time duplication, then you only  write one copy and it's duplicated later (2am). 

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