Easy Raid 0 On Dual Sdhc ?

[Clad]

Hello world !

I was wondering, since the device will have dual SD drive, and you'll probably never take the SD of the devices because of the network-friendlyness of the device (I suppose it will have some kind of internal enabled-by-default FTP server, on top of the package system), would it be possible to have an easy-to-use nice GUI to enable RAID 0 ? (or even RAID 1 for people trusting the device for important non-duplicated datas). Not only it would be faster to make transferts but it'll be easier to manage files with everything on the same logical drive.

Well, that's just a suggestion, and won't prevent me to buy the little wonder even if not available, but I'd like the feature.

 

[sephiroth111]

That would kill the SD card quicker than if it didn't have raid, it was discussed before, something about constant writes or something. i see where your coming from, but i don't think it'd be too practical if the lifespan was significantly reduced because of it.

 

[Clad]

Yeah I know that theorically flash memory have limited read/write per cell.

However, I've been using a raid of 4 CF cards for 3 years now on my main computer (for both the swap and everything but the /home directory) and it's still working like a charm. There is a computer lab near where I live and they also have a few intensivly used computers with flash drives for swap and c:\ drive. (in the win32 world, the c:\ drive is where everything from the OS is, including the swap which is just a large file), all running flawlessly.

The action buttons/d-pad/analog sticks would probably die before the SD anyway. And even if not, SD cards are so cheap and cheaper and cheaper every day.

 

[Pickle]

That would kill the SD card quicker than if it didn't have raid, it was discussed before, something about constant writes or something. i see where your coming from, but i don't think it'd be too practical if the lifespan was significantly reduced because of it.

this thing with killing CF cards is over hyped. Cards are designed to wear evenly, technically you can wear out the card but its unlikely you will do so by the time something new is out. I wouldnt go and put a swap file on the card, but I dont see any problems with raid with 2 cards. Plus cards are becoming so cheap even if you did write heavily to it it could be replaced easily.

In terms if performance, I skeptical if raid would really help. Maybe it will with some real opengl apps show up.

 

[Clad]

Even if the performance boost wouldn't be negligible (not for running applications/emulators/games themselves, but for transferring stuff over the network. You'd basically cut the time by a factor of 2 when downloading a 600mbits divx. With class 6 cards, you'd have to wait 1mn40 to get your file without raid, 50s with raid), it's more about the practicality of seeing your 2 cards on the same logical drive.

 

[StealthBagel]

I've never seen a flash device fail except one that was physically smashed. All this talk of flash lifespan is sensationalistic at best. That said, I don't see a good reason to try and implement RAID0 (in software mind you, with no hardware support at all). Just seems like wasted effort when you could just arrange your files accordingly across both.

My intention, if this device came to fruition, would be to have a System SD card, ~1gb, with basic apps I'd need all the time, emulators, etc. on it and a series of various other 1-4 GB cards (I have lots lying around) for storage of ROMs, music, video, etc. Those would be interchangable. Similar to how I used my PDA a couple years ago, which had a CF and an SD card slot. The CF slot always had a MicroDrive in it and the SD slot was changed out frequently for various tasks.

 

[Mr B]

this thing with killing CF cards is over hyped. Cards are designed to wear evenly, technically you can wear out the card but its unlikely you will do so by the time something new is out.
I don't know what "over hyped" refers to. Its common knowledge that you can kill a flash card by rewrites, it's not a myth, and it's also common knowledge that it takes a lot of rewrites to do it. However, even wear, i cant confirm. Flash memory that wears out, usually gets a few bad sectors at first, and then the problem just grows. If your memory is 75% filled with stuff you never move, or change, and the last 25% is degrading your going to end up with a memory with 75% of the capacity, that will work for a couple of years more. (or all eternity, as long as you leave the data stored, and don't start rewriting it)

I've never seen a flash device fail except one that was physically smashed. All this talk of flash lifespan is sensationalistic at best. That said, I don't see a good reason to try and implement RAID0 (in software mind you, with no hardware support at all). Just seems like wasted effort when you could just arrange your files accordingly across both.
Odd. I have loads of partially damaged flash cards, that has been used for swapdrives, no physical damage, but lots of constant rewrites. When flash were new, i think there was a limit in the area of 1-5K rewrites, today they start at around 10K rewrites. In theory thats 25 rewrites a day, every day, for about 1 year. No name brand, cheap stuff might have lower life expectancy, but i don't know, just makes sense, and someone said it was so in his experience.

B!

 

[Perky_Goth]

Actually, I was going to put swap on an SD card. The problem, according to the internets, is not wear (cheaper cards will be avaiable by the time it wears out), but reading is actually slower unless you buy expensive cards.

My 2c

 

[Clad]

For your regular computer, you don't want to put swap on SDs but on CFs.

 

[Pickle]

QUOTE

I don't know what "over hyped" refers to. Its common knowledge that you can kill a flash card by rewrites, it's not a myth, and it's also common knowledge that it takes a lot of rewrites to do it. However, even wear, i cant confirm. Flash memory that wears out, usually gets a few bad sectors at first, and then the problem just grows. If your memory is 75% filled with stuff you never move, or change, and the last 25% is degrading your going to end up with a memory with 75% of the capacity, that will work for a couple of years more. (or all eternity, as long as you leave the data stored, and don't start rewriting it)



im not saying that continous writing to cf's can cause failure is a myth, but the rate at which it occurs is. In this case for raid 0, the life of the cards isnt going to be any worse than if the cards were not in raid.

I agree with yout point if 75% was full and 25% was always changing then that 25% area is going to fail before the 75%. But say using 100% for a swap, the card will evenly wear giving a pretty good life span.

Ive never had a card die, but I havnt really used them for anything really extreme.

 

[yannv]

I agree with yout point if 75% was full and 25% was always changing then that 25% area is going to fail before the 75%. But say using 100% for a swap, the card will evenly wear giving a pretty good life span.
If you use a write balancing algorithm for your swap, sure. Normally you want quite the opposite - concentrating writes to reduce seeks - so that's not the default for most systems. I'd expect typical flash cards to not do balancing because doing so requires knowledge of what is unused, and they do not parse filesystems.
If we do decide to swap, that's one thing to look into optimizing for flash. For filesystems this has been considered in flash specific ones like JFFS, which essentially uses a circular log structure.