Mirror Robustness

DiskSuite cannot guarantee that a mirror will be able to tolerate multiple slice failures and continue operating. However, depending on the mirror's configuration, in many instances DiskSuite can handle a multiple-slice failure scenario. As long as multiple slice failures within a mirror do not contain the same logical blocks, the mirror continues to operate. (The submirrors must also be identically constructed.)

Consider this example:

Figure 2-5 Mirror Robustness Example

Mirror d1 consists of two stripes (submirrors), each of which consists of three identical physical disks and the same interlace value. A failure of three disks, A, B, and F can be tolerated because the entire logical block range of the mirror is still contained on at least one good disk.

If, however, disks A and D fail, a portion of the mirror's data is no longer available on any disk and access to these logical blocks will fail.

When a portion of a mirror's data is unavailable due to multiple slice errors, access to portions of the mirror where data is still available will succeed. Under this situation, the mirror acts like a single disk that has developed bad blocks; the damaged portions are unavailable, but the rest is available.