Prefetch on spinning disks

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npelov
Posts: 47
Joined: Thu Jun 30, 2016 3:01 pm

Prefetch on spinning disks

Post by npelov »

I noticed that prefetch is fast on SSD, but quite slow on spinning disk even though there is big 60 GB SSD L2 cache. Shouldn't (almost) all the prefetch be already on the SSD?

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support
Posts: 2709
Joined: Sun Dec 21, 2008 2:42 am

Re: Prefetch on spinning disks

Post by support »

Prefetch is to fetch data from underlying disk to L1 cache only.
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Mic
Posts: 3
Joined: Fri Sep 02, 2016 4:49 pm

Re: Prefetch on spinning disks

Post by Mic »

Been noticing this myself as well...

Ok, so I understand that the data written to the SSD is persistent and doesn't actually need to be prefetched. At the same time though, the index (or whatever) of that persistent data does not seem to be retained between reboots - every time I restart, that L2 cache is being shown as completely free. (Side note - I'm actually seeing my prefetch showing as "inactive" in the GUI display, even though it's set in the config?)

Unless I'm misunderstanding that, this is a very serious shortcoming, severely hampering the usefulness of one of the primary purposes of the software. Any plans to alter this behavior?

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