I've just read this in another post about improving RAID5/6 write speeds:

After increasing stripe cache & switching to external bitmap, my speeds are 160 Mb/s writes, 260 Mb/s reads. :-D

I've already found out how to increase the stripe cache and this worked pretty well but I'd like to know more about an external bitmap. I have an incredibly fast (540MB/s) RAID0 SSD that would do well if a bitmap does what I think it does but I'm still very unsure. I've only known about them as long as I've known this post.

A few questions:

• What is a bitmap (in terms of mdadm)?
• What are the advantages of an internal bitmap (over external)?
• What are the advantages of an external bitmap (over internal)?
• How do I switch between the two?

I should add that while this is a I'm-bored-let's-break-something thread, I do value the data stored on the RAID array. If doing this is going to put data at significant risk, please let me know.