Few more SCSI questions
I am now pondering the age-old classic of Raid 5 versus Raid 1/0, on a decent SCSI RAID controller with cache (like mylex 352), with u160 10k RPM drives.
To clarify, I mean a striped set of mirrors rather than a mirrored set of stripes. That setup should be more fault tolerant, unless I am thinking backwards again (a possibility).
In a 4-hard-drive scenario, here are my assumptions:
N=# of drives
S= Storage of each drive
RAID-5 should be ok for things like web-only hosting (mysql/mail on separate box), since it does perform well for small reads. It is only on writes that RAID-5 gets killed, since it must calculate parity info and that slows it down. You would have N-1 * S storage capacity (75% efficient with 4 drives). You have the option to EASILY expand your array, simply by adding more drives to it.
RAID 1/0 should be much better on a mail/MySQL box as its write performance will not be hindered like RAID5. Downside is you cant easily expand the array without rebuilding it. You would basically have N/2 * S storage capacity (50% efficient).
Both systems will offer similar fault tolerance for a single-drive failure. A dual failure would kill the RAID-5, but not necessarily the RAID 0/1, depending on which drives in the array crash.
Either situation will allow for hot-swapping in fresh drives to replace bad ones, with the array automagically rebuilding itself as you wait. RAID-5 will suffer in performance until the new array is rebuilt. RAID 0/1 will not.
Does that all sound correct? Trying to educate myself, and I appreciate the help!
