Update "Fusion-io Introduction" documentation page

This page hasn't been updated in years:

https://mariadb.com/kb/en/library/fusion-io-introduction/

It should probably be updated to reflect current MariaDB versions and/or be merged into other documentation pages.

One specific issue is that it mentions that a "Fusion IO" patch for mysqld is needed to enable atomic writes and safely disable the doublewrite buffer, but it doesn't actually specifically define what this patch is and whether it is still needed in current versions of MariaDB. Based on MDEV-4338, it looks like this patch has probably been built into MariaDB since at least 5.5, so I doubt that any patch is needed anymore.

Another issue is that it recommends the XFS file system with fusion IO devices, but the problem with that is that XFS doesn't allow for atomic writes. There should probably be a more thorough discussion of the advantages and disadvantages of various file systems. NVMFS (formerly DirectFS) seems to be the only file system that supports atomic writes on Fusion IO devices.

https://en.wikipedia.org/wiki/Fusion-io_NVMFS

However, I can't actually find any mention of NVMFS on the SanDisk or Western Digital web sites anymore, so I think NVMFS is probably dead. I was told back in 2016 that SanDisk planned to discontinue support for NVMFS. Here is the information that this person relayed from SanDisk:

SanDisk would like to thank you for your interest in the Non-Volatile Memory File System (NVMFS) and values the feedback you have offered during your evaluation of the technology. As you know, NVMFS has been offered as a free download under ‘Directed Availability’. NVMFS was never offered under ‘General Availability’.

Unfortunately, due to business considerations we regret to inform you that SanDisk will no longer be offering or supporting NVMFS, effective immediately. The official End-of-Life and End-of-Support date for NVMFS is December 18, 2015.

SanDisk greatly values the customers and partners who have downloaded, evaluated, and deployed NVMFS and provided us valued feedback. These relationships allowed SanDisk to further refine NVMFS as a performance enhancement technology.

SanDisk understands the end of support for NVMFS could potentially be an inconvenience for customers who have deployed NVMFS in their environments. Recommendations and possible courses of actions for customers deploying NVMFS are:

1. Deploy a different file system and remove NVMFS (stop using NVMFS)
2. Continue with NVMFS as currently deployed with the understanding SanDisk will not support NVMFS.

SanDisk appreciates your business and trust and will continue working to design and deliver innovative software solutions that enhance the capability and value of our flash hardware products. We look forward to continuing mutual success, and please contact your SanDisk sales representative if there are any questions about this immediate EOL of NVMFS.

So if NVMFS has been killed, then there may not be any supported configurations that allow atomic writes on Fusion-IO devices anymore.

This page will probably also need some changes:

https://mariadb.com/kb/en/library/atomic-write-support/