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Re: innodb_file_per_table on raid 5 server
Posted by: Rick James
Date: October 10, 2015 07:21PM

Well, I disagree.

But first let's decide what criteria you are using:
* Spinning drive? or SSD?
* Hardware RAID controller? or OS software?
* Battery Backed Write Cache? or not?
* Comparing RAID-5 to no RAID? to RAID-10? To Replication for recovery? To DRBD?
* If comparing -5 to -10, are you comparing the same number of drives? or the same capacity?
* What is your goal? High Availability? Recovery from single-drive failure? Other?
* How much does cost matter?
* Fast writes?

If practical, I would go for multiple machines for recovery from a drive failure or a system failure. (Galera distributed across 3 physical locations is currently the best, in my opinion.)

One machine, and you are worried about a single drive crashing -- RAID-5 and RAID-10, those articles notwithstanding, are about the same.

Price per GB with some kind of RAID -- Clearly -5 wins.

Writes -- Both -5 and -10 are likely to do 2 physical writes per logical write. -5 needs to write the block and update the parity (using XOR).

Dispersion of data -- RAID _striping_ (in both -5 and -10) is better than anything to do with manual layout of data vs index, file_per_table, etc.

Read performance of N drives in -5 config is virtually identical to N drives in -10. (Note: the same N, but -5 will have higher capacity.)

A hardware RAID controller with BBWC gives "instantaneous" writes, with no risk of lost data in a power failure. So, regardless of the other factors, I vote for that.

For all the good answers Rolando gives, I am surprised that I disagree with him a non-trivial percentage of the time.

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