Which of the following types of RAID, if configured with the same number and type of disks, would provide the best write performance?

RAID 10 (a stripe of mirrors) provides the best write performance among the choices. This is because it combines the mirroring of RAID 1 with the striping of RAID 0, avoiding the computational overhead associated with parity calculations. For every write operation, data is simply written to two disks in a mirrored pair simultaneously. This process does not involve the read-modify-write sequence, known as the "write penalty," which significantly slows down write operations in parity-based arrays like RAID 3, RAID 5, and RAID 6.

A. RAID 3: Uses a dedicated parity disk that becomes a bottleneck for write operations, as every write must update this single disk, serializing the I/O.

B. RAID 5: Incurs a significant write penalty. Each logical write requires four physical I/O operations (read old data, read old parity, write new data, write new parity).

C. RAID 6: Suffers from the highest write penalty. Updating its dual parity blocks requires six physical I/O operations for a single logical write, making it the slowest.

1. Patterson

D. A.

Gibson

G.

& Katz

R. H. (1988). A case for Redundant Arrays of Inexpensive Disks (RAID). SIGMOD '88: Proceedings of the 1988 ACM SIGMOD international conference on Management of data

109–116. In Section 3

"The RAID Proposal

" the paper details the performance of small writes

noting for RAID 5 (and by extension

RAID 3 and 6) that a single write requires four disk I/Os

a significant performance penalty not present in mirrored arrays (RAID 1/10). https://doi.org/10.1145/50202.50214

2. Arpaci-Dusseau

R. H.

& Arpaci-Dusseau

A. C. (2018). Operating Systems: Three Easy Pieces. Arpaci-Dusseau Books. In Chapter 40

"Redundant Arrays of Inexpensive Disks (RAIDs)

" Section 40.6 discusses RAID-5 write performance

stating

"For each logical write

the RAID controller has to perform four physical I/Os

" which is known as the read-modify-write penalty.

3. University of California

Berkeley. (2014). CS 162: Operating Systems and System Programming

Lecture 14: Filesystems

Disks

and RAIDs. On slide 51

the "RAID IOPS Calculation" table shows that for 100% random writes

the I/Os per second for RAID 10 is N/2

whereas for RAID 5 it is N/4 and for RAID 6 it is N/6 (where N is the number of disks)

clearly demonstrating the superior write performance of RAID 10.