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Simulating Raid 10



I've been trying to decide on what to do with an old Windows 10 PC and I think I've settled on making it a file server using DrivePool. 

I had considered building a RAID machine using one of the various solutions, but I like the idea of having a backup Windows machine available. 

I realize that DrivePool is not RAID software, but it does have many features that are similar. What I'd like to try to do it attempt to simulate a RAID 10 setup as much as possible. 

I'm going to start with four 8 TB hard drives and then add in pairs as needed. I have two old 500 GB SATA SSDs that I can use for caching, but I'm wondering if that is going to be enough. I will be running the server on a 2.5Gbe network. I'd like to be able to saturate that connection, which I think I will be able to do with SSD cache and full duplication. 

Am I on the right track? Is there anything else I should consider? 

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I am trying to wrap my head around your idea. DrivePool works differently than RAID, but I think I can offer some suggestions.

See the source image

Since DrivePool writes full files to one disk at a time, not packets spread over multiple disks, would not standard duplication in DrivePool give you the same result of having a copy of your data on two separate disks?

Essentially, Raid 1+0 is Mirroring with Striping combined. Mirroring for data redundancy, and Striping for speed in a packet writing system. I think you could do something similar in DrivePool using Duplication (Mirroring) on either your entire DrivePool, or just selected important folders, and using 2 SSD's, one each as frontend cache for each duplicate file (Striping) for increased speed. I was able to achieve RAID-like speed on my DrivePool when I added an SSD frontend cache (for WRITES). I also set my DrivePool SSD cache high enough that I can also use it as a very fast READ/WRITE cache for temporary files. I set my SSD cache not to flush until it has 100GB. That's more than I need on any of my temporary working directories.

Another big plus with using DrivePool is that you don't have to add additional HDDs in pairs. I recently built a DrivePool with 3 end-of-life HDDs that I cannot trust on my main DrivePool. I set that entire end-of-life DrivePool to 2X Duplication, In theory, if/when any one drive fails, I'll still have another copy of my files on one of the other 2 remaining HDDs. If there is enough capacity on the remaining 2 HDDs on that DrivePool, it will duplicate the files as needed that were on the failed third HDD. I would never consider using those end-of-life HDDs in a RAID system, but DrivePool lets me get more time out of those old drives. That saves me money and was worth the cost of DrivePool itself.

Another consideration is that a typical RAID system, with packet writing across disks, leaves you with nothing if a HDD fails - unless you build in duplication like your RAID 1+0 setup. You can't read a failed RAID HDD. DrivePool, on the other hand, can often retrieve many, if not most, files off a failing HDD because it contains the entire file, not mere packets. I have been able to retrieve all but maybe 2 or 3 files off a 4TB HDD that crapped out on me. Unless the HDD is totally dead, you have a decent chance of retrieving files off that failing HDD.

Bottom line: To replicate the features of RAID 1+0, use Duplication on your DrivePool for redundancy and add 2 SSDs as frontend cache, one SSD for each duplicate file to be written for RAID-like speed. When you want to expand your setup, in DrivePool you can add one disk at a time instead of having to add disks in pairs.

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DrivePool lets you pool Raid and StorageSpaces volumes ... so it is absolutely possible to create a Raid 10 equivalent.
But it only makes sense for a setup with more than 4 disks/ more than one mirror, otherwise it'd be easier to simply go hardware Raid10 via the mainboard controller (every $80 board from the last decade should be able to do that) or create a striped 2-way mirrored StorageSpace. Onboad controllers usually have enough bandwidth for a 4-disk array and StorageSpaces is pretty robust and performant (as long as it isn't a parity or multi-tier setup^^) so there's no need to go through multiple software layers for a minimalistic array.

That being said, it could still be worth considering if you plan to add drives to the pool/array in the near future. Neither a raid controller nor StorageSpaces will to let you change an existing configuration without scrapping the old array and its data first.
But if you create Raid0 arrays or "simple" StorageSpaces and add those to a pool in DP, you can easily add more striped volumes later for more capacity or more duplication.
You could even upgrade the striped volumes from 2 to 3 or more drives later since it wouldn't affect the mirrors/ duplicated files ... just upgrade one stripe set at a time and let DP add the missing file duplicates back to it.

There will be more overhead tho and striping data via software raid does require additional compute power and available threads on the cpu.
I am not aware of any concrete minimum requirements, but with StorageSpaces in the mix my recommendation regarding older hardware would be: two physical cpu cores/ four logical cores for the OS, DP and networking plus one additional logical cpu core for each striped ("Simple")StorageSpace in the pool. I know it seems like a lot, and you could probably run all of it on an old core2duo and nothing would explode immediately, but the fewer cores available, the more you'll be relying on Windows resource management to do a good job. Heh, yeah ... you don't wanna do that.

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