There have been some recent posts about disappointing performance from G-Raid.
My perspective is that internal is easier (everything in one case, if the case is big enough), less costly (there are very few controllers offering more than 4 external connections), less prone to cables getting loose or tripped over,
The only affordable AND high performance connection for external raids is over SFF-8088. eSATA, USB3, GbE, all are just too slow. Fibre is too costly IMO.
External storage does bring some advantages:
- Better portability and fault tolerance for the system as a whole: if the computer (motherboard, PSU, etc.) is down, the storage box can be connected to another system and you can keep working
- Expandability: internal expansion is limited; external - virtually unlimited (with SAS Expanders)
- Monitoring: individual drives' activity / fault indicators; array status; those may or may not be available with internal storage
- Upgrade-ability: you can upgrade your the main system's chassis w/o touching the storage box
- Service-ability: if you do need to have the storage box sent out for service, it'll be much easier if it's external.
Disadvantages: cost. A good quality 8-bay SAS Expander with a RAID HBA (ARC-1882x): ~$2.3K not including drives. 16-bay - $3K.
Usual advantages of a separate RAID card: performance, advanced RAID modes (RAID6) and features (global hot spares, auto-rebuilding, background initialization, battery backup, caching).
SAS has the same performance whether internal or external though the external does cost more with the storage box. I assume you meant the others excluding SAS. The other benefit to external SAS is the ability to chain multiple External SAS boxes together. The Intel raid controller supports 4 SAS connections deep. With 16 Bay SAS units, that is a massive amount of storage that could not be configured internal.