Going over the solid state offerings for the EMC Clariion lines, Texas Memory RamSans came into the conversation. This was due to the fact that we currently run 2 RamSans in our Environment and consider them the highest tier storage in our datacenters. One is 128 gigs of solid state DRAM storage and the other is 2 terabyte solid state Flash storage with a 64 gig DRAM cache.
Per the title, this is really about the EMC Clariion, not RamSans. Since the RamSan 500 was fronted with the DRAM cache, and the EMC CX4 series contains cache as well, I was curious. I already knew that each Service Processor (SP) in the EMC has 4 gig of cache, and that a LUN can only be active on one SP at a time. Also, per a previous blog post, each DAE has a theoretical max throughput of 8 gigabit per second, 4 gigabit if a single LUN stripes across the whole shelf.
CX4 DAE (general) information
http://blog.colovirt.com/2009/05/29/san-emc-cx4-dae-drive-shelf-information/
As the conversation continued, I was told that typically the Service Processors caching would be disabled on LUNS that reside on the solid state flash drives. In all actuality, I think it should. Being that the typical Clariion implementation will not be dedicated as a solid state SAN, they will have to co-mingle with spindle based hard drives(regular). The throughput is a LOT faster and latency a lot lower on the flash drives. Enabling SP caching on LUNs contained in flash could possibly have a really bad affect on the rest of the system. Being that the cache really speeds up IO for spindle based disks.
Most vendors are toting a 20 physical disks(15kRPM) to 1 Flash disk consolidation
What I am getting at is there seems to be the possibility of flooding the Service Processors cache with flash based storage data, depending on change rate. Since flash is a lot faster, their LUNs would typically be used for databases or high volume services. Even with the ability to do QOS in the CX4 series, disabling Service Processor caching for the flash LUNS looks to be the best solution.
Posted in EMC, Hardware, SAN (Storage Area Network)
