RAID level for servers

[mitchnelson]

How can we know which Raid level is useful for the server E.g Mail, Web, Database server. Also things we can keep in mind before configuring RAID / LVM on live servers.

[Irithori]

Well, analyze the access patterns of your applications, then go for a hardware raid 10 with small (72 or 146GByte) and fast (15k) harddiscs from a tier 1 provider.
At my workplace, we usually have machines with 24 + 24 + 16 harddiscs slots for backend processing.

Present the purchase order to your boss.
If (s)he doesnt get a heart attack: Proceed.
If (s)he does get a heart attack: Get a new boss and try again

[Irithori]

Ok, more seriously:

1) Split your machines by purpose.
Having mail, web and db on one box
- results in a more random IO pattern
- is harder to distribute to separate raids
- and also introduces dependencies: If the DB get´s dumped, the webservers might also suffer

2) Analyze your application.
For example mysql:
Random access to the DBs, sequential write access to the binary logs, seq write access for the DB dumps.

3) split IO load
For the mysql example: a raid10 like described above for the DBs, and a raid5 each for the logs and dumps.
Add a little raid1 for the system and you have a good start.

4) DBAs do not like lvm or anything between their DB and the bare metal for that matter.

5) Each hardware is a bit different, do some IO stresstests and application benchmarks to find the sweet spot in regards to filesystem (or lack whereof), filesystem options, blocksize, etc.

6) Load.
How many users/connections/load do you expect and what kind of machinery do you have? The higher the load, the more aggressive performance optimizations are needed.