Long live the Flash Drive-Wear Leveling

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volkswagner
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Long live the Flash Drive-Wear Leveling

Post by volkswagner »

This is a new topic for me.  Although I have used flash media, never have I run an OS from one.

I don't want to invest in flash drives, then watch them parish.

I would like to list some precautions, and preparations for running the OS and utilizing swap space.

Wiki

Looking for facts on the hardware level protection built into the device, BIOS settings, and software settings.
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Foxx
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Re: Long live the Flash Drive-Wear Leveling

Post by Foxx »

Ive been playing with embedded stuff for a little while, and to be honest I am consider myself a novice, but until I design my own device from the chip level up, I will always think this. Anyways...

One thing that should be noted with Embedded devices is the Flash Wear, as volkswagner mentioned. For those of you whom don't understand this term, let me explain.

A typical flash chip these days, weather it be SD card, Compact Flash, or the onboard 512MB on the WebDT is comprised of logic NAND gates. These gates can only be written to so many times before they wear down and burn out. Constant writing to a NAND Flash device will kill it, and many OS' will require this to operate properly.

The best thing for an embedded device is to run a Read-Only Realtime OS (RTOS) that will not constantly keep writing the the NAND. A good example of an OS that would work are many of the Live Linux distros' like Knoppix, Damn Small, Puppy, and Backtrack. You can pass a boot parameters to not use Swap Space (aka Page File for Windows) thus eliminating the worry of burning out your Flash. Also Win CE, Windows Mobile, and WIndows Embedded can be used and set up to turn on the Extended Write Filter (EWF) so it will not wear out the host drive. I have used Linux from Compact Flash as a Read Only drive to load the OS to RAM only, using Damn Small, and with enough RAM the otherwise crappy Tablet (Gateway Connected Touchpad) didnt run too badly... Unfortunately I see no easy method in upgrading the WebDT System RAM, but that's another topic.
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david_halliday
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Re: Long live the Flash Drive-Wear Leveling

Post by david_halliday »

Many flash devices now have wear leveling build in so will last quite some time. I am not sure if this is the case with the internal flash on the dt366. If however you are concerned you could always run main OS / and /usr of the internal disk in read only mode and mount /var and /home on a CF card. CF cards are cheap and easy to replace. If you find that you still want to write to / and /usr you an also use a unionfs (or tranlucent fs) to a filesystem on the CF card. This will overlay a writable area over the mostly readonly / and /usr.

Dave.
Foxx
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Re: Long live the Flash Drive-Wear Leveling

Post by Foxx »

What causes NTLDR to disappear? Any clue?
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angrymeat
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Re: Long live the Flash Drive-Wear Leveling

Post by angrymeat »

windows xp likes to lose its ntldr randomly  happens on desktops pcs as well  . I have had it happen from bad suspends  or pc's turned off while suspended . With the way these devices are used in  the real world I can see where it would happen alot .
Foxx
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Re: Long live the Flash Drive-Wear Leveling

Post by Foxx »

I dont have that issue often on my desktops and laptops, but yeah, NTLDR can be a bit bitchy in general. I figured it might have been a direct issue with the WebDT not liking Windows XP (Embedded, Tablet, Whatever).

Thanks for the input. I am still taking a whack at building WinXP Embedded for the WebDT, but this is my first blind forage into WinXP Embed'.
Hacking is not a crime, It's a passion - www.BSoDtv.org
If you need someone to IDE mod your DT366 toss me a PM.
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