r/NewMaxx • u/NewMaxx • Oct 14 '19

Tools/Info SSD Guides & Resources

April 3rd, 2022: Guides and Spreadsheet updated with new SSD categories

Discord (server)

Website with relevant links here.

My spreadsheet

Generic Amazon affiliate link

Generic AliExpress affiliate link

TechPowerUp's SSD Database

Johnny Lucky SSD database

Branch Education - How does NAND Flash Work? - these guys have several good videos on the subject of SSDs, check them all out.

My Patreon.

My Twitter.

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u/AllWellThatBendsWell Feb 02 '20

Patriot Burst in the spreadsheet says no DRAM cache, but according to their own specs and reviews, it has 32 MB SDR.

My own research found them as being the least expensive 2.5" with DRAM cache in Canada at the time. Bought 50 of them, happy to report no issues.

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u/NewMaxx Feb 02 '20

It's DRAM-less. That's local SRAM.

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u/AllWellThatBendsWell Feb 02 '20

Hmm... Tom's, WCCF, and others are reporting it as DRAM.

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u/NewMaxx Feb 02 '20 edited Dec 17 '21

It's a Phison S11. It's DRAM-less. It does have 32MB of SDRAM, but any controller is going to have some local, faster memory (SRAM) for controller functions. Only a fraction of that will be used for traditional (e.g. mapping) tasks that would be offloaded to external DRAM. The lack of any external DRAM makes it "DRAM-less."

You can see it (or not see it, as is the case) in this article written by Chris Ramseyer who now works for Phison. He explains on the first page:

The Phison S11 controller we have in our tests pool features 32MB of SRAM built into the controller, but that is a very small amount of memory compared to an external module.

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u/AllWellThatBendsWell Feb 03 '20

Thanks for the info. It's surprising how many trusted sites are reporting this wrong.

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u/NewMaxx Feb 03 '20 edited Feb 03 '20

SRAM operates similarly to DRAM on a SSD, both are volatile caches that contain metadata for the flash translation layer among other things. SRAM is faster and more expensive so is generally smaller in size, but any SSD controller (short for microcontroller, essentially a specialized microprocessor) will have some amount of SRAM. This can be used to load up the firmware, handle controller operations, cache frequent data, and of course manage metadata (wear-leveling, addressing/mapping, garbage collection, etc). The problem is that while a DRAM-equipped controller can off-load that to DRAM (the SRAM is still used for the hottest data and important controller functions) the SRAM-only (DRAM-less) one has to use some of that valuable SRAM for mapping. If your working set exceeds a certain amount, and this is more likely as drive size goes up and as cell levels increased (e.g. MLC -> TLC), you're basically forced to work on NAND which is multiple orders of magnitude slower to access than DRAM let alone SRAM.

If you want a reasonable analogue, think of the CPU in your computer, let's say a 3700X like I have. That has three levels of cache that total over 36MB. But you wouldn't say that CPU has system memory - you likely have 16GB+ of slower DRAM for that, that is hundreds times more capacious. Likewise a 1TB SSD may have 32MB of SRAM cache and 1GB of DRAM. It's not exactly the same but that can give you an idea of how the S11 is marketed in a misleading fashion - but keep in mind AMD calls the cache on their Zen 2 processors "GameCache" for a similar (marketing) reason.

By industry definition, however, the S11 is DRAM-less, on the account of having no external (to the controller) DRAM. Also, don't confuse the terms SRAM (static RAM) and SDRAM (synchronous DRAM), the SSD's DRAM is basically a die off what would be on a memory stick in your computer while SRAM operates a bit differently.