I am in the process of implementing AFTD in NW 7.6.3 (up to this point I've just been using tape). I'm hoping someone has some recommendations for how to set it up.
I would like to clone backups daily to tape to send offsite, but keep the backups on the AFTD for about 4 weeks to have quick access for restores.
From what I understand, once an AFTD is full, if a backup is in process, it will not move to the next AFTD like it would with tape, even if the AFTD is labelled in the same pool. In other words, savesets cannot span AFTDs.
I also gather that if an AFTD is full, NetWorker will delete expired savesets on that AFTD and then continue the backup.
If this is true, would it be best to create a large (multi TB) AFTD and just let NetWorker delete expired savesets to create room for new backups? What would be the the advantage of having several smaller AFTDs?
When multiple AFTDs are in the same pool, you won't have control over what backup set goes where and if there is concern that AFTD may fiil, then it is better to use bigger one.
There is a feature called "AFTD load balancing", where you can adjust the target and max sessions attributes per device to balance the data load for simultaneous sessions more evenly across available devices. These parameters specify the maximum number of save sessions to be established before the NetWorker server attempts to assign save sessions to another device.
For AFTDs, all volumes, depending on the selection criteria (pool settings), choose the AFTD with the least amount of data written to it, and join sessions based on the device's target and max sessions. If the number of sessions being written to the first device exceeds the target sessions setting, another AFTD is considered for new backup sessions and is selected from the remaining suitable AFTDs. The AFTD that is selected will be the AFTD with the least amount of NetWorker data written to it. The least amount of data written is calculated in bytes (not by percentage of disk space used) and only bytes that were written by NetWorker are counted.
I forgot to mention the space management of the AFTD device. There is a configurable setting for determining at what capacity the NetWorker software should stop writing to an AFTD spans from 1 to 100%. Setting the value to 0 or leaving the attribute empty in the AFTD Percentage Capacity attribute is equivalent to a setting of 100%. This means that the entire capacity of the filesystem can be used for the AFTD volume.
When set, the AFTD Percentage Capacity attribute is used to declare the volume full and to calculate high/low watermarks. Whenthe percentage capacity attribute is modified, mount and re-mount the volume for the new settings to take effect. The level watermark is calculated based on the percentage of restricted capacity, not on the full capacity of the filesystem.
Hope this helps you.