# Systematic Literature Review of Challenges in Blockchain Scalability
## 6 RQ1: How Scalability Issue Can Impact Blockchain Implementation?
Besides the inefficiency in the transaction verification process, another crucial factor of importance is storage, which needs to be seriously considered [5]. As transactions grows, the required storage capacity for blocks needs to scale up at tandem. It is reported that currently, Bitcoin storage is more than 305.23 GB [8], Ethereum is at 667.110 GB [8], and LiteCoin at 28.45 GB. It should be mentioned here that energy consumption is also a crucial issue in public blockchain implementation. When comparing the consumption of electricity by Bitcoin with other cryptocurrencies, Bitcoin was in the 49 th position [5]. It is interesting to note that actual consumption of electricity by Bitcoin is less than the predicted scale, which may suggest that the Bitcoin could not scale well per expectations and predictions. The combination of all the limitations mentioned above is apparently degrading the performance of public blockchain decentralized applications. The low throughput, high latency, high storage, and high energy consumption cannot satisfy the large-scale implementation of blockchain in time-mission-critical or real-time applications. The Internet of Things (IoT) is a technology that is growing aggressively, and it is embracing blockchain as an integral component in IoT security applications. IoT was tagged as \"The Global Infrastructure of the Information Society\" by ITU in 2015 [14]. Besides the many benefits, IoT has some limitations. Public blockchains have been technically considered to address those issues by decentralizing computation powers, processing, and storage. Unfortunately, public blockchain is still suffering from scalability matters in IoT applications [33; 34]. Principally, public blockchain technology is not suitable for lightweight IoT devices. In blockchain, a node is supposed to verify every transaction and perform search in every block, likely an extremely heavy load for lightweight IoT devices. As discussed earlier, public blockchains require massive resources to support their operations and are highly constrained by consensus delay, making it almost impossible to deploy them in small/low spec IoT devices. It would not be possible for IoT devices to verify a transaction without a massive amount of historical data. IoT therefore needs to either carry high storage by itself or rely on a centralized server. While considering the large-scale storage requirement in public blockchains, it is worth to also examine the financial aspects. For example, in Ethereum, it costs 2 \(\times\) 105 US Dollars per gigabyte of data storage, making it probably highly expensive to implement IoT networks with blockchain [35]. The storage requirement for the IoT network is very much dependent on the types of application. As such, the overall data storage size could be destructive in IoT-enabled blockchain since each block would be replicated n times in the n-node public blockchain networks. For example, in smart city application, vehicular traces of 700 cars for 24 h demand a storage capacity of close to 4.03 GB, which is about 0.24 MB per hour per car [36]. In public blockchains, high latency can be due to transaction confirmation. This behavior may cause inconsistency in a decentralized environment. The usual tolerated latency in blockchain is not suitable in many IoT applications. For example, in Bitcoin, the confirmation time is 10 min, which can be an extremely long delay for sensitive IoT applications such as vehicular networks. In the light of all these limitations, it is obvious that scalability issue is persisting and degrading the performance of IoTs enabled with blockchain.