Oracle Tips by Burleson

Oracle Disk I/O Tuning

Chapter 5: RAID and RAID Administration

Mirrored Stripes or Striped Mirrors

This RAID level is often misunderstood. Which should you use, RAID 10 or RAID 0+1? Let us examine Fig 5.10 and see exactly how they work. In the case of RAID 0+1 (also called mirrored stripe), striping is implemented in the lowest position, meaning from a group of drives. A stripe is formed and then two such stripes are mirrored resulting in a logical drive. With this method, the loss of any drive makes the entire stripe invalid and the stripe is detached from the mirror pair. When the failed disk is replaced, the entire stripe must be brought up to date. Recovering the entire stripe can take a substantial amount of time as all the stripe members need to update the data.

Fig 5.10 Mirrored Stripe and Striped Mirror RAID architecture

With RAID 1+0 (or 10), mirroring is implemented at the lowest position. A group of mirrored drives are used to create a stripe. RAID 10 (also called a striped mirror) is the superior method. If a disk fails in a striped mirror layout, only the failing disk is detached, and only that portion of the volume loses redundancy. When the disk is replaced, only a portion of the volume needs to be recovered. As shown in Fig 5.10, mirrored drives are independent units. When a disk is lost, it affects only one mirrored pair.

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