MySQL uses disk. Ok, so everybody knew that. MySQL uses disk in two primary ways.
- Random I/O (Reading & Writing Data/Index blocks)
- Sequential I/O (Binary Log, InnoDB Redo Log)
Historically it’s been best practice to separate these onto
different spindles, and also separating the OS and tmp space onto
a third spindle. With commodity H/W that can be easily done, but
today a lot of people use SAN. Is this a good thing for a MySQL
Database?
That’s a topic of much discussion at a later time, however I’ll
add two points. A lot of SAN configurations are RAID 5, and RAID
10 is a better choice due to removing the requirement to
calculate the parity. Second, last week I observed a RAID disk
failure and it took an incredible long time for the disk to be
re-built. Just how many SAN uses our there have actually timed a
disk rebuild on a loaded system and seen the impact on the system
in general.
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