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In what cases is a DRAM-less SSD good enough? (lemmy.ml)

submitted 8 months ago by geoma@lemmy.ml to c/hardware@lemmy.ml

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Where I live, DRAM-less SSDs are a lot cheaper (half the price). Most sources online say "go for an SSD with DRAM". But I wonder, are cases in which a DRAM-less SSD will do just fine?

My main focus is resurrecting old laptops (from 2006 to 2015), installing GNU/Linux and an sometimes investing in an SSD will give them a performance boost, but the budget is limited because I can't sella uch an old laptop at a non very budgety price.

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[–] Blue_Morpho@lemmy.world 0 points 8 months ago (1 children)

I don't even understand how dram ssd would be significantly faster outside of benchmarks.

The OS caches everything to PC dram and sends it out to the SSD. So adding more ram to your PC would have the same effect.

In benchmarks, the dram ssd appears to be much faster by return control to the OS much sooner. But a non dram ssd is getting data from PC cache dram via dma and that's not impacting CPU load. So it's not really improving the speed.

[–] moody@lemmings.world 3 points 8 months ago (1 children)

It allows the drive to be used more quickly. If you've ever tried using a computer while the disk is at 100% usage, you'll have noticed that anything you do that requires disk access slows to a crawl. With DRAM on the drive, it takes more to overload the drive and makes smaller transfers nearly instant, as data gets buffered into the much faster DRAM rather than directly to the SSD.

Like I mentioned though, in most cases the average user won't notice a difference. If you really want to squeeze a bit of extra performance out of your drive, that's where you'll want the DRAM. If you're just trying to get old laptops running well again, it's basically a non-factor.

[–] Blue_Morpho@lemmy.world 0 points 7 months ago* (last edited 7 months ago) (1 children)

It allows the drive to be used more quickly

But not anymore so than adding the same amount of dram to the PC. It's cpu->cpu dram->SSD dram->ssd. It will only show a performance difference on benchmarks or if your PC ram is completely full. You could get more performance by adding dram to the PC and telling the OS to never go below X amount of disk cache.

makes smaller transfers nearly instant, as data gets buffered into the much faster DRAM rather than directly to the SSD.

That's not actual speed but benchmark speed. A copy is going to PC cache and then gets written out to the SSD. Having SSD dram allows the SSD to say "done" sooner to the OS despite it taking the same total time.

[–] dgriffith@aussie.zone 1 points 7 months ago (1 children)

Having SSD dram allows the SSD to say "done" sooner to the OS despite it taking the same total time.

That's exactly why. When writing to a drive the OS waits until the disk says "done" and then goes about it's business.

If the drive then takes an extra bit of time internally to write to permanent storage that's none of the OS's business as long as it can pull that written data from "somewhere" and deliver it to the OS if asked.

[–] Blue_Morpho@lemmy.world 2 points 7 months ago* (last edited 7 months ago)

But it gets "done" immediately when you have write caching enabled and the file fits in ram. Which is on by default for non removable storage. It's only benchmarks which disable write caching in order to separate PC performance from the drive being tested.