Using incr-only strategy can result in backup failures in degraded mode of operation

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Backups of DLEs fail in degraded mode (when there is a backup device failure) if incr-only strategy is used
The strategy options in amanda.conf configuration file impact the operation of planner process during backup run. It has influence of which backup level size estimates are asked for from the Amanda client. Normally Amanda can ask estimates for level 0, level N, and level N+1.
When strategy noinc is specified, then Amanda will only ask for a level 0 (full backup) size estimate.
With strategy incronly, will normally not schedule a size estimate for level 0, except when forced (with amadmin <configuration_name> force).
Amanda usually also makes a "plan B": when the writing to device fails, it falls back to degraded mode, and will do some incrementals instead of full backups to the holdingdisk. Restricting the estimates using strategy option influences this phase. When "strategy noinc" was specified, these DLE's cannot be written to media device in incremental mode and will fail completely.