PostgreSQL 12 High Availability Cookbook - Third Edition

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We mentioned controller cards earlier and noted that they also offer onboard cache. RAID has been around for a long time, and though disks are getting much larger, they haven't experienced an equivalent increase in speed. In scenarios that use RAID 5 or 6, writes can also be slowed since each write must be committed to several devices simultaneously in the form of parity.

To combat this, RAID controllers allow configuration of the cache to buffer writes in favor of reads, or vice versa. Don't be afraid to adjust this and run tests to determine the best cache mix. If everything else fails, start with 100% for writes, as they are the most in need of caching. Keep a close eye on write performance and give it priority if possible. ...