Yeah I'm using a scandisk also but a 16g class 10. Great cards and hold up well. As far as the extra partitions/Ssm and swap. Mine is 1.5 g sdext/ 512mb ext4/ 512mb swap rest vfat. Unlike data mode where the system no longer uses the internal storage for any part of newly installed apps, you are only limited by the space of the sdcard. Running SSM on the other hand does still use internal storage, Dalvik-cache (if I remember correctly) so you are limited on the amount of apps you can install internally by whatever is left after the rom install. I think I only had maybe 65mb or so after flashing CTmod. The point is making a large ext4 partition, anything over 512mb) your never going to use running ssm and if you switch back to data mode you allready have it partitioned to the max you want to use for swap.
Swap I believe I had explained a couple of posts back on size and the reason being and yes you have the correct mmctblck. The Prevail, as far as i can tell, will never swap out more than a couple hundred k at the very most, and honestly through exp i dont believe it will even do that. Thats why in reality the 256mb that cwm allows for the swap partition is more than enough. I had did alot of research before even flashing my first rom. I am on MokeeMod now.
I have always been plagued with the fc's issue sometimes worse than others, no matter what rom I'm on. The Prevail is a cheap pos but great for learning how to flash roms, hacking etc.. or as a backup .
I am currently having issues with not being able to charge the battery while installed in phone so it looks like I will be purchasing another device also. Not spending $100 on another prevail, will put towards the sv1 or even can get an sg2 for $100.
Hope this helps and sorry your having the issues you are. It does sound like probably the device itself is just worn out, never had issues with flashing roms or it not taking to data or Ssm modes. Always been a very easy process but I am by no means an expert Just started doing this a couple of months ago myself so please talk with one of the other more experience guys like lv, cwhatever,wetbiker7. I'm just trying to PIF like these guys did for me.
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