Fortunately for us RAID is quite mathematical in its performance
RAID 0, as we know is the number of drives * speed. Therefore with 2 drives you get 2*speed of the drive.
With RAID 5 however, you are dealing with a slew of factors such as overhead computing power, RAID card performance and the stripe size you have allocated(128kb etc).
Knowing this, the typical RAID 5 array will display performance = (n-1) * speed. This is because you are keeping one drive for correctional parity information, and only the other two spindles actually record data.
You may be thinking now that you should get the speed of two drives(like in RAID 0) but we haven't factored in the RAID card's capabilities and the time it takes to process the parity information into meta-data.
Therefore, if we were to compare a RAID 5 array to a RAID 0, the following comparisons would immediately be apparent.
- Reduced random read speed(but only by a small amount)
- Drastically reduced write speeds(of course, there is a huge CPU overhead here on the RAID Card)
- Fault tolerance of 1 drive(over 0 in RAID 0).
- Of course read//write speeds will depend on the stripe size you have set up, if you wish to know about how stripe size affects the performance of your array post back.
Hope this has been helpful in some way.Edited by Razultull - 4/16/11 at 7:13am