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Preallocating files is very slow on SSD cache for some reason


Tarh
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Hi! So playing with the SSD caching and a torrent client, I realized that for some reason file preallocation is always done at around 32MB/s on a SATA SSD. Which is much faster even on a HDD. No other software interference, raid controller, cable quality, trim, wear or any issues exist and write caching is of course enabled. I know because if I manually start moving the same files it does it with multiple hundreds per seconds a megabyte - as it should - during this very slow prealloc. So there's no hardware bottleneck. And no, we're not talking about thousands of tiny files, they are all 1GB+ files a piece.

Now, I'm not 100% sure it's DrivePool's fault, but then again, even after many hours of various tasks and benchmarks I can't reproduce any slowdown on the SSD.

And since qBittorrent is preallocing files much faster on a HDD, I'd hazard a bet that it's not its fault. I've adde an SSD cache to be faster, yet it's slower than my bandwidth so something is very wrong here.

 

https://i.imgur.com/57CPrI7.png

So what is going on, why is this so unbearably slow?

 

Edit: I just learned the "increase priority" fast-forward icon while balancing (well hidden) today, so is it possible prealloc is being limited by some option here?

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DrivePool only uses part of the SSD in the hidden PoolPart directory, so you can still use the SSD outside of the DrivePool envieronment. Have you tried the preallocation to the SSD itself - outside of DrivePool - and compared that to the preallocation speed of that same SSD within DrivePool?

I don't use qBittorrent on my system, but the programs I do use have not shown any difference between writing to DrivePool's SSD cache compared to writing to the SSD by itself. For myself, I was happy to verify that the programs I use were not slowed down by going through DrivePool. In fact, in all the testing I have done on file transfers to DrivePool or directly to the SSD/HDDs, I have not seen any difference in speed. 

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