Since this issue appears frequently in the Veeam forums, I decided to recap in this post all the settings you can set in Veeam to better use an ExaGrid appliance:
Inline deduplication: ON
ExaGrid is the only dedup appliance where, as of today, combining Veeam and its own deduplication gives some advantage; in other appliances this only leads to wasting time doing it twice
Align backup file data blocks: OFF
ExaGrid is not affected by variable data blocks. Keep this off anyway to reduce the load on the Veeam proxy
ExaGrid has its own algorithms, and can compare data from different Veeam backup jobs; this leads to better dedup and compression ratios than veeam, that compares only data inside the same job.
There is only one scenario where you can leave compression on, only if you then also enable in the repository advanced settings also “Decompress backup data blocks before storing”; this is when you place the ExaGrid appliance off-site, and you use two proxies to do backups. First will be places in the source site and will compress the data, the second one will be placed in the target site and will decompress data before saving them in the ExaGrid; this will anyway receive NON compressed data.