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Replace expensive SSDs with camera memory?

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a c 311 G Storage
January 22, 2010 12:32:29 PM

I'm wondering what other people might think of this:

Fast flash SSDs are expensive per GB. We all know that. On the other hand, I can walk out and buy cards at about $4/GB that have a minimum read/write speed of 60 GB, with maximums twice that, if I go to a camera store and buy SDHC. The next proposed standard is SDXC, and (from Wikipedia) "The maximum transfer rate of SDXC was announced as 104 MByte/s, with plans to increase it to 300 MByte/s in the future."

Should we just have little boxes that look like SD card readers but have RAID controllers? Plug in eight or twelve of those little guys and run like the wind? Would this work? Be cheaper / faster than the current SSD drives? Let me know what you think, please.
January 22, 2010 12:45:31 PM

People have already been down that route before SSD's became more common and "affordable".

SSD's have a number of important features such as Controlers that have wear leveling algorithyms to improve reliability of the devices and can deal with bad clusters etc and other factors which add cost.

What you are talking about does work for a while, but you may well end up loosing data and killing the SD cards quite fast with an operating system running off them

a c 415 G Storage
January 22, 2010 3:54:29 PM

There are two problems with camera memory cards:

1) They're slow. A Class 6 SDHC card has a guaranteed write rate of only 6MB/sec, less than 1/10 that of a typical SSD. A high-speed SDXC interface by itself doesn't mean the cards themselves are going to be any faster - and those cards that *are* faster will be more expensive. And even if they use the fastest possible flash chips, a single memory card can't compete with an SSD which uses several chips internally in a RAID-like configuration.

2) They usually connected to a computer system with USB, which itself limits the maximum transfer rate and has latencies which work against the flash memory's access time advantage. USB 3.0 may help this situation somewhat.
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a b G Storage
January 22, 2010 5:00:15 PM

Memory cards also don't support DMA transfer, so while reading/writing the host will hang.
a b G Storage
January 22, 2010 8:14:38 PM

WyomingKnott said:

Should we just have little boxes that look like SD card readers but have RAID controllers? Plug in eight or twelve of those little guys and run like the wind? Would this work? Be cheaper / faster than the current SSD drives? Let me know what you think, please.

Forget about using SD to make a cheap SSD. If you're serious about this you should use CF.
It uses an interface very similar to P-ATA which means you can convert it to a regular P-ATA drive by using a small, cheap converter. Then you will have all the advantages of a regular P-ATA drive. You can connect them in a RAID configuration, use the onboard P-ATA interface which is 4x faster than USB and requires less CPU power and it's detected as an internal hard drive (no boot issues).

The problems: a fast card costs much more than $4/GB. About $10/GB for 60MB/s cards and about $15/GB for 90MB/s cards.
The second and biggest problem: random writes are extremely slow with these cards. We're talking about 30ms average for the fast cards. That's three times slower than a regular hard drive and probably 100 times slower than a SSD.
a c 311 G Storage
January 23, 2010 11:55:48 AM

Thanks to all for the feedback. It's reasonable; otherwise enthusiasts wouldn't be snapping up these SSDs.
January 23, 2010 5:43:35 PM

MrLinux said:
Memory cards also don't support DMA transfer, so while reading/writing the host will hang.


what do you mean by "host will hang"?

I just transfered a few hundred megs of data to my micro-sd card and nothing changed. I remember PIO mode on a floppy drive hanging a computer, but I have no trouble with card readers.

Also, during the transfer my highest CPU usage was ~3%, but I do have ~25 tabs of Chrome opened.

Patriot and others already demo'd 90MB/sec USB 3.0 flash drives. Would be nice with ReadyBoost.

But I agree, you get what you pay for. Use an actual SSD for a harddrive or anything important.
January 26, 2010 11:59:57 PM

SD cards won't hang the Cpu because they're connected to a separate reader. And CF cards, a less bad choice, do have Udma. By the way, SD cards exceed by far 6MB/s: 18MB/s here on a completely banal one.

CF cards do have wear levelling now, and SD as well. And their Flash chips are the same as in an SSD; better, CF are available with SLC chips, while SSD with SLC are very expensive.

But CF lack the onboard Ram and the corresponding controller programme optimization which allow a SSD to keep write requests in a queue until it can fill the whole write page. This is what makes SSD's acceptable fast write rate and swift write access time (just Ram!), and this is even more important with Mlc. I know no single CF that has one. Accordingly, write access time is around 20ms for a CF, and parallel write requests don't improve the throughput - while an Hdd or a Ssd is very good at that.

That's why booting on CF is generally disappointing. A good 3.5" 7200rpm is a bit faster than a good SLC CF (Lexar 300x, Adata 266x, Transcend 266x, and very few more; 25usd for 2GB). Most CF (using MLC) are much worse than any Hdd.

Some P-Ata Raid controllers have Ram onboard, but they lack the write algorithm adapted to Flash, and add time at boot.

This is also what made early SSD so bad (better that a 2.5" 5400rpm, but much worse than a 3.5" 7200rpm): they lacked the good Ram+controller+microcode.

Though, I use a CF on a laptop. P1 120MHz, 40MB Ram, with Mw-dma2. There, a good CF is way faster than a 2.5" 5400rpm 6GB... Boots W95b in 20s instead of 60s. But did you write "Core i7, Seven, Sata/3000" and the like?
January 27, 2010 12:03:32 AM

And Ssd aren't that expensive any more, because you can now get older used ones. Like a 30GB Vertex (fast!) for 90usd at eBay.com or eBay.de. At that price, it's worth every pence. Better invested than in a Cpu.
a c 415 G Storage
January 27, 2010 6:41:19 AM

To be clear, the notion of non-DMA devices "hanging the CPU" is a bit ambiguous. What they're saying is that without DMA the CPU will need to execute a number of instructions to move each and every byte to or from memory when you're reading or writing. The net effect is that whenever you read or write to the drive the CPU will be 100% busy (or close to it) and therefore won't be able to do any other useful work at the same time.
February 16, 2012 1:07:25 PM

I thought that a regular usb stick had also a processor to divide the writing to random unused places, so is that not the same with sdcards ?

Now I bought a 32GB sdhc card class-10 for 40 euro, with nand technology, which should not have the wearing of a old type, I heard.

Anyone still against using sdhc as ssd?
February 19, 2012 3:05:50 AM

I asked this exact question yesterday, the idea just suddenly came to me and I went out and bought an SD card just to play around with the idea.

I know for a fact, especially in notebooks, my HDD maxes out at around 70 MB/s sequential and 40 MB/s around real word scenarios.

But this new SD card promises read/writes up to 95 MB/s
System wide, my write performance won't change using this card as a cache drive.

But this card is for sure at least twice as fast as my HDD.

Repurchasing windows, and only getting 'some' of my programs onto an SSD isn't worth the mess of trouble that it is. I even have a 2nd drive bay but that has its catches too (missing proprietary cable).

I haven't done anything scientific, but my computer 'feels' faster with this card.

Finally, high end, professional grade SD cards have memory controllers just like SSDs do. Saying they don't have controllers or don't have wear-leveling is absurd
The 'home run' would be if the OS loaded things from both drives simultaneously. That's at least 2x speed upgrade for anything with an SD slot
!