Ошибка проверки ...
NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
struct statfs tStats;
float availableDisk = 0;
if (statfs([[paths lastObject] cString], &tStats) != -1)
availableDisk = (float)(tStats.f_bavail * tStats.f_bsize);