RAID 1 systems consist of two drives. The second drive is an identical copy of the first drive this allows for redundancy - if one drive fails then the system will continue to work with the remaining drive but in what is known as 'degraded' mode. Below is a diagram of a RAID 1 pair of drives.
RAID 1 is best suited for critical systems that must have zero or very little downtime. For example, an eCommerce - web server, if this were to fail then your business would start losing money the moment it failed. With RAID 1 in place the server would keep running after a single drive failure and a spare drive could be inserted and rebuilt automatically without any downtime.
The drawbacks of RAID 1 are that writes to the drives are take longer as for each change there are two writes and two verifies, however reads are similar to that of RAID 0 where a controller can be set to read ahead. This means that when data is read, the blocks are read as if it were a RAID 0.
MjM Data Recovery offer a no recovery no fee for all our services including RAID 1. Please phone us on 0800 072 3282 and ask to talk directly to one of our RAID engineers.