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Disk on Module SLC vs. MLC

Shadow Lord

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I was perusing eBay DOM for a replacement drive on my Pentium 200MMX drive and I noticed that now you can get both MLC and SLC based units. The price difference is negligible ($10 on an 8 GB unit). However, is it worth it? That is I doubt the performance difference would be noticeable (or more likely non-existent) between the two on a system that old. However, how about wear and longevity? SLC is supposed to last 10x longer then MLC and as I doubt most DOM MLCs have a sandforce controller for wear leveling the inherent longer life of an SLC maybe the way to go. Any one have first hand experience? Thanks.
 
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Stone

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I don't have any experience but based on what I've read I'm in agreement with your analysis. For typical use the difference is negligible. I you think wear and longevity might be an issue then SLC might be a better choice.
 

Chuck(G)

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Be careful with eBay. Some of the cards advertised as SLC are MLCs--I ran into this myself. Likely, the "negligible difference" in price indicates this.

SLC (I have some) has considerably more longevity due to a cell recording a single logic level, versus MLC, which uses several logic levels to encode more than one bit in a single celll. So if you shop eBay, double-check what they're selling if they claim SLC. There's a lot of counterfeit out there.
 

Shadow Lord

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I you think wear and longevity might be an issue then SLC might be a better choice.

Hopefully, the SLC will outlast my Pentium 200MMX

Be careful with eBay. Some of the cards advertised as SLC are MLCs--I ran into this myself. Likely, the "negligible difference" in price indicates this.

Chuck,

The thought did occur to me as SLCs are supposed to be 2-3x as expensive as MLCs. However, outside of trusting our friendly Chinese digital store keeper or cracking one open post purchase how can I determine if it is really a SLC?
 

pearce_jj

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Buy two, fill and erase one 10,000 times and see if it still works ;-)
 

eeguru

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Current NAND geometry is typically 2500-3000 cycles per cell @ 55C = 1 year retention. You always have to factor in temp and time when talking about NAND wear.

The primary consumers of parts are cell phone and tablet companies. There's a lot of price volatility outside that realm. So it could explain why a legitimate SLC part is the same price. Of course there is no way of knowing unless you break open the plastic and lookup the raw NAND part number. And even that chip could have a reprinted label or otherwise be fake. So unless you have some Nitric acid, protective gear, and a microscope.. there isn't a good way to know other than to trust your supply chain.

The MLC part is definitely MLC. The SLC is likely SLC but may not be. Go with the later if they are the same price.
 

Shadow Lord

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The MLC part is definitely MLC. The SLC is likely SLC but may not be. Go with the later if they are the same price.

Which brings me back to my original question is it worth it? I.E. while the SLC part, if real, is better would an MLC part due just as well for a vintage system getting minimal use (say turned on once a month for a few hours)? BTW: if anyone is interested here are the two items I am looking at -

SLC

MLC
 

glitch

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If you're not concerned about having a SATA drive in there, find a bootable add-in card and grab a SATA SSD. You can also go for a name-brand DOM from a company like M-Systems or PQI. Their write tolerances and predicted data retention are published in their design specs. I've had excellent results with products from both companies, mostly using them as hard disk replacements in vintage computers, or as working media in Linux and FreeBSD based network appliances.

I don't know how common it is with DOMs, but I've been burned *many* times with buying cheap CompactFlash media on eBay. That's actually part of why I switched to DOMs!
 

Shadow Lord

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Well,

I checked out the manufacturer's web site and they sell two versions of the SLC modules:

KDM-40VS.1-XXXGSS is listed as SLC NAND while the KDM-40VS.2-XXXGSS (the one being sold on eBay) is listed as MLC/SLC NAND. So is that a hybrid/mix of cells explaining the lower price?

EDIT: To Answer my own question:

SLC MLC Hybrid SSDs
In June 2008 - Silicon Motion announced a new family of flash SSD controllers which enable oems to mix and match MLC and SLC chips in the same drive.

The controller can analyze the incoming files from the host and intelligently move frequently accessed data to SLC NAND and non-frequently accessed data to MLC NAND. With this innovative hybrid architecture, the SSD system cost is significantly reduced to a level comparable to a pure MLC-based SSD, while endurance is significantly enhanced and comparable to a pure SLC-based SSD.

However, the intrinsically higher susceptibility of MLC flash to electrical disturbances remains a risk factor in such hybrid devices.

Quoting from here.
 
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eeguru

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Most MLC parts have a high endurance SLC cache. However make no mistake, they are MLC parts. And SLC and MLC are just interpretations of the amount of additional voltage needed to turn on the floating gate (Vth). You can have a part with mixed cell interpretations.

And for vintage computing, it's especially important to use a better quality part (eg. SLC). You aren't writing frequently so you are more concerned about the 'fade' case. You can't just sit a flash part on a shelf and come back years later and expect your data to be there. Every single NAND cell in the world has an expiration date. Every time you re-write that cell, you reset the expiration date but the expiration timer gets shorter each time. SLC has longer expiration times because you have twice the Vth margin. But you are storing only one bit per cell instead of 2 (MLC) or 3 (TLC). So it's less capacity per sq silicon area. (eg more $).
 

Shadow Lord

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And for vintage computing, it's especially important to use a better quality part (eg. SLC). You aren't writing frequently so you are more concerned about the 'fade' case. You can't just sit a flash part on a shelf and come back years later and expect your data to be there.

That is an excellent point that I had not considered. So heeding Chuck's warning and the fact I can find any reliable info/security on eBay where can I reliably get an SLC DOM?
 

Shadow Lord

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If you're not concerned about having a SATA drive in there, find a bootable add-in card and grab a SATA SSD.

I was actually trying to avoid putting in a HDD in there if I could. Otherwise, IDE drives are cheap and plentiful (not to mention there is a functioning one in there already).
 
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