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Simple Questions?


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I have what I think is a simple question ...

 

Happily running Stablebit Drivepool now for about a month, new whs 2011.  Runs great, no issues.

 

As far as balancing go, I have noted other topics that said that it was not balancing.  I have seen your replies that basically said there is a high threshold to trigger rebalancing.  All of that makes sense.  I know you offer the equalizer plug in as well for those that want a truly even distribution across disks.  

 

My question is this:

 

 1) My current pool is only about 33% full at this point.  I recently added a new drive to the pool.  For about 2 weeks now, there is nothing on that drive - 0.0%.  I've played a bit with the balancers, but have not been able to convince DrivePool to add any data to that drive.

 

 2) It seems like I could download and use the volume equalizer to accomplish this.  Is that correct?

 

 3) More philosophically, why does DP choose to NOT utilize newly installed disks and more aggressively balance the pool?  It seems from reading some of your other posts, read striping and disc I/O would be improved by being able to read from more than one disk at the same time - thus it seems that having the data spread over more disks should confer some type of advantage.  Perhaps very small, but an advantage nonetheless.  And wouldn't having the files more "spread" result in lower disk temperatures, less wear, etc.?  If I am wrong, I'd love to understand why.  It would seem to me that the equalizer plug-in would then be the best thing .... no?  

 

 Is the equalizer just there to provide a cure for my neurosis at seeing one drive with 60% used and another with 0%? :-) 

 

 Thanks!

 

 rmf

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Yes, you will need to download the disk space equalizer and use that to automatically balance the pool.  Volume equalizer is for when you have multiple volumes to equalize on the same physical disk.  The plug in architecture is in place so that you can decide how your data gets distributed across the disks in your pool, and you can even write your own balancer if you want to.  Not everyone wants automatic balancing; some want DrivePool to fill up one disk at a time, or any number of different options.  

 

I use the disk space equalizer as the 1st balancer and set to equalize by percent used and including both un-duplicated and duplicated files.  If you want balancing to only occur at a certain time, then you can schedule it.  My pool is primarily used as file storage and for media streaming, so balancing does not impact me.  If you were to use it for something like virtual machine or database storage, then performance is paramount and automatic balancing may negatively impact it in those cases.

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You've neatly summed the "pros" of aggressive equalizing - improved I/O and read striping, etc. However, if all of your drives are equally accessed and suffering equal wear, then (at least in theory) you have an increased chance of all of your drives failing at the same time. That's obviously not desirable.

 

Another "con" is that any single given file cannot be split across disks, so  if your aggressively balanced pool is close to full you might not have enough space to write a particularly large file even though your total free space is many multiples larger than what you need.

 

While both of these "cons" are unlikely (but as I can personally attest, not impossible), having the default settings be conservative is good protocol. Let the user decide what is acceptable risk. :)

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If you add new files to the pool they will be placed on the new drive (the drive with the most free space). Adding new files to the drive with the most free space is how Drivepool by default does it's disc space balancing and it's a slow process but it will balance itself out over time...

 

Regarding disc temperature it depends on your enclosure :)  If the discs are sitting right next to each other then having two moderately used discs will output more heat then one very active disc. So unless you have good cooling the temperature will become higher the more active discs you have (theoretically). And if you have good cooling then you need not worry...

 

Also if you're concerned about disc wear then you should also consider that constant aggressive balancing will incur a lot of read/writes from moving files back and forth between discs just to get that "perfect" distribution so it might actually do the opposite of what you were aiming for.

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Thanks everyone for your responses.  

 

Reading through and thinking about things, I think it's probably a "push" on aggressive balancing vs. letting DrivePool decide where things should go.  

 

To clarify - Henrik - the behavior you describe (adding new files to the pool --> to the new drive) is not what is happening.  New files added are being added to the largest drive (perhaps because it has more free space than the other drive with 0% utilized) rather than the empty drive.  

 

I decided to impose a lower "limit" to fill a drive before diverting data - i.e. instead of waiting until 90%, I asked it to balance when a drive is more than 60% full.  This resulted in moving of data from all drives with >60% utilization to the drive with 0% utilized.  So maybe it's a compromise between aggressively balancing the data and letting them fill up on their own.  

 

In any case, congratulations on a great product and a great community to support it.  Keep up the good work!

 

 -rmf

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