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Related Optical

  Stor2
  Imager 1
  Imager 2
  Imager 3
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   Striping?
   What is
   RAID, RAIT or
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Contact us to configure an Ultera solution to fit your needs
What is Mirroring?
Mirroring Solutions
dot.gif (333 bytes) Tape Drives
dot.gif (333 bytes) Tape Libraries
dot.gif (333 bytes) Optical Drives
dot.gif (333 bytes) Optical Libraries
Description
dot.gif (333 bytes) Operating Modes
dot.gif (333 bytes) Theory of Operation
dot.gif (333 bytes) Custom Variations
Tape Mirroring Example using 5 independent Tape Drives

Mirroring Animation

Operating Modes

Mirroring - simplifies Disaster Recovery Plans by writing the "data" to up to five separate drives simultaneously.
Operating Mode Number of Tape Drives Tape
RAID
Level
Description
Fault
Tolerant
Mirroring 2 2 1 Mirroring 2 Drives Yes
Mirroring 3 3 1 Mirroring 3 Drives Yes
Mirroring 4 4 1 Mirroring 4 Drives Yes
Mirroring 5 5 1 Mirroring 5 Drives Yes
Paired Mirroring 4 1 Mirroring 2 Drives,2 Independent Drive Sets Yes

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Theory of Operation

The Tape RAID Level-1 operation is referred to as "Tape Mirroring" (or data duplication).  Each block of the users data is written to a specific set of array channels (referred to as a "Mirrored set") at the same time.  The controller maintains the tape positions for all drives within a mirrored set (up to 5 drives).

User data is read from the lowest channel number within the mirrored set.  The array controller handles read/write errors differently depending on the settings of the disaster recovery options.

If a write error is encountered with any one of the drives within a mirrored set and the fault tolerant write option is enabled, the failing drive is disabled on the fly without interrupting the backup process.  The controller reports a write error only upon detecting a write error from "all of the drives" within a mirrored set.

If a write error is encountered with any one of the drives within a mirrored set and the fault tolerant write option is disabled, the write error is reported to the host.

If a read error is encountered with any one of the drives within a mirrored set and the fault tolerant read option is enabled, the failing drive is disabled on the fly without interrupting the restore or verify process.  The controller reports a read error only upon detecting a read error from "all of the drives" within a mirrored set.

If a read error is encountered with any one of the drives within a mirrored set and the fault tolerant read option is disabled, the read error is reported to the host.  The array controller does not attempt to recover read errors using other available drives within the mirrored set.

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Custom Variations
Mirroring Mode 1 - Mirroring
Requires both cartridges to be loaded for backup and restore operations. Errors from any drive are reported to the host system.
Mirroring Mode 2 - Disaster Recovery Option 1
Requires 2 cartridges for backup operations.   Supports single tape restores from the primary drive on channel 1.  Write errors are reported to the host system.
Mirroring Mode 3 - Disaster Recovery Option 2
Requires 2 cartridges for backup operations.   Supports single tape restores from the primary drive on channel 1.  Write errors are reported to the host system.  Write errors with one drive disable that drive and the backup continues without interruption
Mirroring Mode 4 - Fault Tolerance
Requires both cartridges to be loaded for backup and restore operations. Errors from either drive disable that drive and the backup or restore operation continues without interruption.

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