What are the theoretical performance differences between a single disk and a RAID-10 array?

Question

Not taking hardware RAID cards into account, what kind of theoretical performance improvements should I see when using 4 disks in a RAID-10 array vs 1 disk by itself?

For example, on RAID-0, I would expect to see something like singleDrivePerformance * driveCount, as reads and writes are spread out pretty evenly across all physical disks in the array. On RAID-1, I'd expect to see singleDrivePerformance / 2. Does this mean that with RAID-10, I should see double the performance of a single drive, albeit with parity?

Answer 1

On RAID-1, I'd expect to see singleDrivePerformance / 2.

Why? Writes have to go to both drives, but with two drives you can write twice as much data, so the write speed should the same. Reads can come from either drive, so read speed should be doubled.

Does this mean that with RAID-10, I should see double the performance of a single drive, albeit with parity?

For a four-drive RAID 10, for sequential reads, you should see four times the performance. You can read from all four drives at full speed. For non-sequential reads, it will somewhere between twice the performance (if all reads come from the same two drives) to four times (if they're better distributed).

Sequential writes should be twice as fast. All data has to be written twice, but with four drives, you can write four times as much. Non-sequential writes will be somewhere between twice as fast (if they evenly divide over both pairs) to the same speed (if they all have to go twice to the same pair).

Answer 2

Depending on your RAID driver the perfomance increase differs, but basically:

On RAID 0 (striping) your read and write performance goes up by the number of drives, because one half of the data is on one disk and the other half is one the other disk.

On RAID 1 (mirroring) your write perfomance stays the same, because data has to be written to both disks. But your read performance can go up by the number of disks, because data can be read independently from each disk.

Compared to a single drive the performance of a RAID10 or RAID01 (both requiring 4 drives) read perfomance goes up by 4 and write performance by 2.

There is no parity on RAID 0 or 1.

check wikipedia, it basically says the same.