In terms of performance and availability, which is the better, RAID 4 or RAID 5?
With respect to performance, RAID 5 will generally outperform RAID 4. With RAID 4, you have a dedicated parity drive, which means that the parity drive will be a bottleneck in high I/O situations. RAID 5, however, spreads not only the data but also the parity information across all drives in the RAID set. So, although there is still overhead in undertaking a parity calculation per stripe, the I/O is spread evenly across all drives as each stripe is written (no one drive is a bottleneck).
With respect to availability, RAID 5 will provide the same amount of protection as RAID 4.
However, there is a caveat to this discussion, in that this assumes that everything remains equal in the comparison. There are storage arrays that are built to provide optimal performance for one type of RAID set over another, or can be tuned to provide better performance than usual for certain types of RAID sets. I would suggest consulting the storage array manufacturer in such a case.
Nevertheless, usually RAID 5 seems to be the most reasonable catch-all RAID scheme that provides the best compromise between performance and protection until either one or the other becomes more important.
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