test

    dispatch_queue_t queue = dispatch_queue_create("somequeue", DISPATCH_QUEUE_CONCURRENT);
    dispatch_apply(1000000, queue, ^(size_t i) {
        
        NSUInteger length = [self saveSomethingToDisk];
        NSUInteger gotLength = [self getSoemthingFromDisk];
        
        if (length != gotLength)
        {
            NSLog(@"Something went wrong!");
        }
        
    });

tests

- (NSUInteger)saveSomethingToDisk
{
    NSString* cachesPath = [NSSearchPathForDirectoriesInDomains(NSCachesDirectory, NSUserDomainMask, YES) lastObject];
    NSString* someFile = [cachesPath stringByAppendingPathComponent:@"somefile"];
    NSData* data = [NSData dataWithContentsOfFile:[[NSBundle mainBundle]  pathForResource:@"apple_rainbow_logo" ofType:@"jpg"]];
    
    BOOL ok = NO;
    
    @try
    {
        ok = [NSKeyedArchiver archiveRootObject:data toFile:someFile];
    }
    @catch (NSException *exception)
    {
        NSLog(@"Got an exception archiving");
    }
    @finally
    {
        NSLog(@"written %@", ok?@"OK":@"FAILED");
        
        return data.length;
    }
}

- (NSUInteger)getSoemthingFromDisk
{
    NSString* cachesPath = [NSSearchPathForDirectoriesInDomains(NSCachesDirectory, NSUserDomainMask, YES) lastObject];
    NSString* someFile = [cachesPath stringByAppendingPathComponent:@"somefile"];
    
    NSData* data = nil;
    
    @try {
        data = [NSKeyedUnarchiver unarchiveObjectWithFile:someFile];
    }
    @catch (NSException *exception) {
        NSLog(@"Got an exception unarchiving");
    }
    @finally
    {
        NSLog(@"retreived %@",data?@"OK":@"FAILED");
        return data?data.length:0;
    }
}