PostgreSQL 12 High Availability Cookbook - Third Edition

Saddling up to a SAN

Those familiar with the industry may have encountered NAS as well. How exactly is that different, and how is it relevant to us?

It's subtle but important. While both introduce networked storage, only a SAN grants direct block-level access, as if the allocation were raw, unformatted disk space. NAS systems operate one level higher, providing a fully formatted filesystem such as NFS or CIFS. This means our PostgreSQL database does not have direct control over the filesystem; locks, flushes, allocation, and read cache management are all controlled by a remote server.

When building a highly available server, raw I/O and synchronization messages are very important, and NFS is more for sharing storage than extending the storage ...