I worked at several x86 Linux + SPARC Solaris shops between 1999 and say 2011. Linux was always on the app servers, and Solaris on the DB servers.
The Sun hardware was just better, more robust, and the machines tended to have hot-swappable bits. Better support for fast storage. Hot-plug in Linux was bad and took time to get good. The hardware was cheap, and took time to get good. Ditto driver support. It just got better and better until there was no reason to buy Sun.
And then Oracle bought Sun, and there was now a reason to _avoid_ Sun.
The Sun hardware was just better, more robust, and the machines tended to have hot-swappable bits. Better support for fast storage. Hot-plug in Linux was bad and took time to get good. The hardware was cheap, and took time to get good. Ditto driver support. It just got better and better until there was no reason to buy Sun.
And then Oracle bought Sun, and there was now a reason to _avoid_ Sun.