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Penryn

Questions on DrivePool behavior

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I've been stalking out a good replacement for Windows Storage Spaces and am interested in DrivePool's behavior as an alternative pooling solution. Since it's file-based and not block-based though, I was wondering:

 

1) Suppose I have large, changing files like an Outlook .pst or virtual hard drives stored on the pool with duplication enabled. What happens when the file is modified/appended to? Does the entire file need to be duplicated again? ie: does it get copied again in its entirety to other drives or does it do something fancy like rsync's rolling hash strategy to calculate differences and update each file incrementally?

I'm trying to avoid saving gigabytes of information every time I use a .vhd or when Crashplan backs up, since Crashplan relies on many 4GB files.

 

2) What happens when a drive begins to fail for some reason and an error occurs while reading a certain file? Does DrivePool pull the file from another drive?

I ask because I've experienced corruption from a SMART failure on a drive recently which made reading certain files from a pool error out. This should have been solved by pulling the file from a different drive in the pool but it didn't.

 

Thanks!

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I can only speculate. I *think* Drashna has stated that SQL Server databases can be stored on duplicated Pools and I _assume_ that that means that I/O on parts of the database files are done concurrently, not one first and then a full copy to the other, but I am not exactly sure. I *think* DP "simply" causes the required I/O operation to occur on both copies, so just the additional I/O neccessary. Again, not sure.

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I've been stalking out a good replacement for Windows Storage Spaces and am interested in DrivePool's behavior as an alternative pooling solution. Since it's file-based and not block-based though, I was wondering:

 

1) Suppose I have large, changing files like an Outlook .pst or virtual hard drives stored on the pool with duplication enabled. What happens when the file is modified/appended to? Does the entire file need to be duplicated again? ie: does it get copied again in its entirety to other drives or does it do something fancy like rsync's rolling hash strategy to calculate differences and update each file incrementally?

I'm trying to avoid saving gigabytes of information every time I use a .vhd or when Crashplan backs up, since Crashplan relies on many 4GB files.

 

By default, "Real Time Duplication" is enabled on StableBit DrivePool. Unless you have a specific reason (and some people do), then we recommend that you leave it enabled.

 

What Real Time duplication does is that any time a file is created, modified, moved, copied, etc... the file is written to both destination disks in parallel. This means that there are no issues with locked files, or the contents changing while duplicating, etc.  

 

This includes modifying and appending to files.

You can run databases, and even Virtual Machines off of the pool, if you wanted. In fact, I believe that Alex (the developer) does so. 

 

I've also ran MySQL server off of a pool at one point (mostly to see how well it worked). I moved it back, because ... well databases run better from a SSD. :)

 

2) What happens when a drive begins to fail for some reason and an error occurs while reading a certain file? Does DrivePool pull the file from another drive?

I ask because I've experienced corruption from a SMART failure on a drive recently which made reading certain files from a pool error out. This should have been solved by pulling the file from a different drive in the pool but it didn't.

 

Thanks!

 

This really depends on the situation. But for the most part, it will just error out on the file. This is handled this way to ensure that the file contents do not get out of sync, as that could be even more problematic.

 

As vfsrecycle_kid indicates, StableBit DrivePool will evacuate the contents of a disk if StableBit Scanner marks the disk as damaged (unreadable sectors). You can optionally set this for SMART errors as well.

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Thanks so much everyone, especially Drashna!

 

I decided to bite after seeing how robust Stablebit's stuff seems to be, and how good the community is here. I've gone from DriveBender to Storage Spaces and now to DrivePool all for the sake of being able to handle dying drives. I think Stablebit Scanner is exactly what I've needed in conjunction with pooling this whole time.

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You are very welcome!

 

And I'm glad to hear that you are very happy with the products and the community!

 

Also, check out the "StableBit Scanner" balancer, in the balancer options in DrivePool. There are some fine tuning settings you may want to check out (just to customize to your preferences).

 

And if you have any other questions, don't hesitate to ask.

 

Regards

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