Mirrored Cache
A cache memory that has duplicate data from another controller. In the event of failure of the original controller, the second controller can take the cached data and place it on the disk array.
Mirrored Hard Drive
Two hard drives the computer sees as one unit. Information is stored simultaneously on each drive. If one hard disk drive fails, the other contains all of the cached data and the system can continue operating.
Mirroring
The complete duplication of data on one disk drive to another disk drive, this duplication occurs simultaneously with each write operation: each disk will be the mirror image of the other (also known as RAID Level 1, see RAID Levels). All Mylex RAID controllers support mirroring.
MTBF
Mean time between failure. Used to measure computer component average reliability/life expectancy. MTBF is not as well-suited for measuring the reliability of array storage systems as MTDL, MTTR or MTDA (see below) because it does not account for an array’s ability to recover from a drive failure. In addition, enhanced enclosure environments used with arrays to increase uptime can further limit the applicability of MTBF ratings for array solutions.
MTDA
Mean time between data access (or availability). The average time before non-redundant components fail, causing data inaccessibility without loss or corruption.
MTDL
Mean time to data loss. The average time before the failure of an array component causes data to be lost or corrupted.
MTTR
Mean time to repair. The average time required to bring an array storage subsystem back to full fault tolerance.
Member (disk)
A disk that is in use as a member of a disk array.
Cache memory is the data buffer or cache between the hard drive and the actual platters in the drive where data is temporarily stored. Access to data in the memory cache is much faster than accessing data on the platters in the hard drive. The larger the memory cache, the more data can be stored which can be accessed faster. A drive with 16 MB of cache will perform faster than a drive with 8 MB or 2 MB of cache because more data can be stored in the cache on the 16 MB cache drive.