6.4 Index Size During Migration

When a migration begins, Retain creates a copy of the current index, thus temporarily doubling the space consumed by the index. After the migration completes, the old index can be removed and space reclaimed.

Also, the new index may be larger than the current index, due to the increased power and abilities of the new indexer. How much change there is, depends on the composition of the current archive, any limits set in indexing attachments, and how many attachments there are in the archive. If there are a lot of attachments, or very large attachments, then the increase in size is significantly larger than if there are small or a limited number of attachments in the archive. With no limits on indexing attachments and a lot of large attachments in the system, an increase of up to 4 times the current index size is possible. With limits included, the new index may be smaller after upgrading. For the upgrade and a worst-case scenario, ensure that up to 5 times the current index size is available before starting the index migration. (With a current index size of 5 GB, ensure that the volume has a minimum of 20 GB free before starting the migration.) The average increase is expected to be around 20%.

If there is insufficient space to perform the migration, Retain moves into maintenance mode until more space is provided. Retain 4 checks for free disk space on the storage, index, and system locations. If there is less than 20 GB free space, Retain sends a warning message every 6 hours. At 10 GB of free space left, Retain enters maintenance mode and all jobs are disabled. To exit maintenance mode, you must provide more free space on the volume.

NOTE:It is important to recognize that migration time and performance depend mostly on the performance of the storage system. External storage systems, such as appliances, may 'prioritize' seldom-used data to low performing storage and have a negative effect on migration performance. In addition, file systems of existing storage largely dictate how fast indexing, migration, and message view can be performed. To ensure high performance, house the storage on performance hardware with a performance file system.