Depending on what time of day it fails, the bad disk is generally replaced within 2-18 hours. Copying the data onto the new disk, from the remaining half of the

Depending on what time of day it fails, the bad disk is generally replaced within 2-18 hours. Copying the data onto the new disk, from the remaining half of the original pair, typically takes another day or so. But the material found on the failed disk usually remains available throughout the replacement process because both original copies are on live servers. Read requests are ordinarily divided more or less evenly between the two. If one copy dies, requests are simply all directed to the other copy until the lost one is replaced. There is no ability to "write" (make changes) to any affected items during the replacement process, but they usually remain readable throughout.