Why is it not recommended to use RAID 5 for a log file? While reading SQL Server Query Performance Tuning written by Grant Fritchey, I found it difficult to understand the following part: avoid RAID&nbsp;5 for t-logs because, for every write request, RAID&nbsp;5 disk arrays incur twice the number of disk I/Os compared to RAID&nbsp;1 or RAID&nbsp;10.

I know that RAID 5 differentiate from other RAIDs with its parity feature. It means that if some of the drives fails, then it is possible to recover lost data from the other drives. I want to understand why it is not recommended to use RAID&nbsp;5 for a transaction log file. Explanation in the book was not enough for me to get it. Maybe someone could explain it to me or provide a good article.
Transaction log writes, when they occur, are synchronous operations, that is, the activity that has caused a log write must wait until log I/O completes before continuing to do whatever it is doing. As a result log writes are very sensitive to the write throughput of the underlying storage.

As you have mentioned, every write to a RAID-5 device has an overhead1 of calculating and writing a parity block in addition to the data block(s). However small, this extra work RAID-5 performs on each write operation is the reason behind the recommendation to not use RAID-5 for log storage.



1 - More details in this Q&amp;A