Data Domain: Best practices for placement/cabling of an external ES30 solid state disk (SSD) shelf/enclosure

Data Domain Operating System (DDOS) 6.0 introduces support for a single external ES30 enclosure/shelf populated with solid state disks (SSDs) for use as a cache tier/metadata on flash. Note that:

• The SSD shelf/enclosure is only used as cache for the Data Domain File System (DDFS) and alternate shelves containing standard hard drives (HDDs) must still be attached to the system for normal data storage
• A system can only have a single SSD shelf/enclosure attached
• SSD shelves are only supported with certain Data Domain controllers (EOS T3/T4 and Apollo systems)
• These guidelines do not apply to EOS systems using SSD devices within the controller itself (they only apply to use of an external SSD enclosure)

To ensure optimal performance of the SSD shelf/enclosure (and therefore the wider cache tier) there are a number of best practice guidelines which should be adhered to:

• Ideally the SSD enclosure should be attached to the Data Domain controller on its own SAS chain/loop. This means that the only I/Os being performed on the chain/loop (and by the corresponding SAS ports) are to low latency/high performance SSD devices giving optimal throughput
• If it is not possible to attach the SSD enclosure in its own chain/loop (for example all other chains/loops are already fully populated) then the SSD enclosure should be the first enclosure on its chain/loop with standard HDD enclosures being added after the SSD enclosure. Note that performance of the SSD shelf will not be optimal as I/Os on the chain/loop will be a mix of high performance I/O to SSD devices and 'slower' I/Os to standard HDD devices
• The SSD enclosure should not be attached to an existing enclosure chain/loop after HDD enclosures as this will force all high performance I/Os to SSD devices to traverse multiple 'hops' (SAS expanders) introducing additional latency to these operations

For further information see the corresponding Data Domain controllers 'hardware overview and installation guide'.