Looking For Feedback On A Sd Card Idea


aranson

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So, I came up with this idea a few days back, but immediately dismissed it on basis that it was pretty silly to impliment. It keeps coming back, so I thought I would ask.

1) How difficult would it be to mount both SD cards as a single mount point?
2) If it could be done, would it provide any read/write speed advantages (ie: what is the bottleneck in the SD read/write, is it the SD cards themselves or is it the bus)
3) Are both SD cards on the same bus, or do they each have their own?

The idea, of course, is to get two identical (well, the same make and model) 8 GB (or so) SDHC cards, and link them to a common mount point. According to the Pandora, it now has 16 GB of data storage. You could transfer data to and from the USB port (again I wonder how fast that would be... maybe ftp would be the best idea there) to offset the fact that you (obviously) can't use the SD ports to transfer files.

The first cool thing that it would do is create a device with a single pool of data (like an eee, or even an iphone), so you don't have to worry about splitting your MP3 or movie collection. An added benifet may be an increase in read/write, but that seems a little sketchy. Could you convince the kernel to "raid" the two cards? Even if you could, would it provide any speed advantage. Or, you could partition your Pandora (but... why!) any other way you want to.

Of course you are taking a gamble on your data. If one of the cards fails, data on both cards are toast. All you would have to do is create a program to back up your data to say a network drive, or a even a desktop computer. That way if you wanted to upgrade your Pandora's "Flash Hard Drive" from a 16 GB to a 24 GB all you have to do is get a single 16 GB, reformat the two cards (again make and model problems may occur) and restore from backup.

I think that a modular SD storage system would be pretty cool.

Any thoughts or ideas about this would be appreciated.
 
I'm not sure what the advantage would be (not having a dig your idea, just trying to understand what you're getting at). With the ability to use 2x32GB cards simultaneously, surely all our requirements are covered?

There's a discussion here on the SDHC RAID idea: http://www.gp32x.de/board/index.php?showtopic=39854

And just because it popped into my head, a SATA SSD enclosure that allows you to RAID your own CF cards. http://www.engadget.com/2008/05/24/sans-di...5-inch-enclosu/ (Not all that relevant to the discussion, just cool).
 
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Go with your initial feelings - it's pretty silly.

Yes, it's technically possible to do it. No, you won't get any noticeable speed increase from RAID0 due to system overhead (it may actually run slower). JBOD makes more sense than RAID0, but not by much. You still have an increased chance of data loss, and you lose the ability to swap out one card without losing access to the other.

Setting up your SD cards in an array might seem cool from a "Gee, look what I can do!" standpoint, but it is just too inconvenient and risky to use on a daily basis. Go ahead and set it up - you'll be switching back within days.
 
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If it was a hassle to replace SD cards (like if they were screwed into the machine) you might have an advantage in the sense that you could get a larger "disk" by doing this. But since SD cards are easily swappable, it's actually much more of a hassle to deal with swapping cards in and out of an array/JBOD, particularly if files are striped or partially spread across cards. Much much easier to just have multiple cards.

The basic idea isn't bad (I JBOD/EVMS2 basically every Linux machine I build now) but with SD cards it's just not worth it.
 
Here's my question... If this were possible, and if it were implemented. So you have two 8 GB SD cards acting within the Pandora as one 16 GB SD Card (or one 16 GB HD, or however it would look)....

How do you use them outside the Pandora? Would they work just like any other SD card in your laptop or desktop, or would you have to have both of them plugged in to work, or would using just one corrupt the file structure?

I really don't know the answers to these questions - hence why I am asking. But, to me, part of the appeal of having SD storage is the ease of transfer between devices - and the fact that I can carry 5 or 10 of them and swap stuff out. From what you are saying, I'd have to replace both cards every time. So I couldn't be listening to an mp3 off of one and then swap the other out to get my next game ready or whatever.
 
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