Space, performance, and MTTDL JAN 30, 2007
The worst thing about a model is that it is a simplification of real life.
Small, Random Read Performance Model
- Rotational Speed (rpm)Maximum Rotational Latency (ms)4,20014.35,40011.17,2008.310,0006.015,0004.0
- For dynamic striping (RAID-0), add the iops for each set or disk. On average the iops are spread randomly across all sets or disks, gaining concurrency.
- For mirroring (RAID-1), add the iops for each set or disk. For reads, any set or disk can satisfy a read, so we also get concurrency.
- For single parity raidz (RAID-5), the set operates at the performance of one disk. See below.
- For double parity raidz2 (RAID-6), the set operates at the performance of one disk. See below.
RAID Configuration (6 disks)
Random Read Performance
Relative to a Single Disk
6-disk dynamic stripe (RAID-0)
3-set dynamic stripe, 2-way mirror
2-set dynamic stripe, 3-way mirror
6-disk raidz (RAID-5)
2-set dynamic stripe, 3-disk raidz
2-way mirror, 3-disk raidz
6-disk raidz2 (RAID-6)