Ok - so really this is best done in person with someone who can demo and animate the block allocations for you. BUT Compellent storage is virtualized by Tier - so for each tier of storage (which are defined by disks of like I/O characteristics such as rotational speed, flash type, etc) uses all of the devices within it to process each I/O.  Compellent's allow each LUN to have multiple RAID algorithms in use at the same time. The ideal on this would be to have write operations occur in RAID 10 (the fastest for write) and read operations to happen from RAID5/6 (most space efficient). RAID types do NOT reserve a specific amount of physical disks - but rather function as a method for organizing blocks from various LUNS across all of the disks within a Tier. Data Progression (Tiering) extends this capability to allow volumes to exist with blocks in multiple tiers based on the age and activity of each block. The LUN is presented such that there is no difference to servers based on the placement of data and the blocks can be shifted dynamically as criteria are met. Recently Data Progression was expanded to allow the mix of write optimized and read optimized SSD tiers which changes the economics around Flash Arrays without resorting to using SSD as a front end cache. The data is moved more quickly then a normal progression from the write optimized drives to the read optimized SSD so as to keep performance levels above 100K IOPS while leveraging the cost differences inherent to MLC drives (they are cheaper). [URL]~data-sheets~en/documents~dell-compellent-software-suite.pdf One thing that really sets Compellent storage apart is that the license is NOT tied to the hardware. So an SC8000 controller can be replaced without purchasing more licensing or invalidating the original license. Licensing is perpetual and abstracted from the hardware that is being used. So if I have a Compellent I bought 5 years ago with licensing for all the features for 16 disks I can apply that license to SC8000 controllers and SSD drives (up to 16 non-spare) and start using it. I think if you use this site as your jump off point - [URL]  you will find plenty of information - you just have to look at the Storage Center software rather than specific hardware building blocks.
Hi. We are looking into buying a Dell Compellent Array, but before that im looking into its technology.  Unfortunately the few public datasheets on the SC8000 are very brief. Im looking into information how the array handles its raids, from what ive understood, when you create a volume, some data will be placed on raid 10, some on raid 5 and some might end up on raid6 (tiering). But how are these raid levels defined? Are they simply made from all available disks of a certain type, say raid10 is ssd and SAS-NL is raid6. or are they raids built more like how 3par handles CPGs, creating mini raids out of chunks of the different disks? HP also has a wealth of information readily available about the 3par arrays, i cannot find anything for compellent :( [URL]
Compellent Volumes raid levels