RAID1 (Mirror For Data Backup) 2 HDDs Need Selecting Above

In RAID 1 (mirroring without parity or striping), data is written identically to multiple disks (a "mirrored set"). While any number of disks may be used, many implementations deal with only 2.^{[citation needed]} The array continues to operate as long as at least one drive is functioning. With appropriate operating system support, there can be increased read performance, and only a minimal write performance reduction; implementing RAID 1 with a separate controller for each disk in order to perform simultaneous reads (and writes) is sometimes called multiplexing (or duplexing when there are only 2 disks).