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Dell first to market with TLC drives for enterprise flash arrays

Dell SC series storage customers will be able to use TLC flash drives, which are suited to read-intensive workloads, from August in arrays with MLC, SLC and/or spinning disk

Dell is the first storage array maker to offer TLC (triple level cell) flash drives, which will be available for its SC series arrays from August 2015.

TLC flash brings a lower cost of flash storage for the customer as its packs more data into the same footprint as MLC flash, which is the current de facto standard.

However, because of the increased complexity of TLC, the process overhead for writes is significantly higher and wear is increased. For that reason, TLC is best suited to read operations, especially sequential ones.

Dell will therefore market TLC drives for its arrays as Mainstream Read Intensive and will target customers who might otherwise opt for 15,000rpm spinning disk, claiming the price point of TLC flash to be comparable.

“We've talked about democratising flash, and this is us pushing it out to the suburbs. We're making an economic argument that TLC is a replacement for 15,000rpm and possibly 10,000 rpm spinning disk in terms of cost,” said Paul Harrison, Dell UK storage director. 

“Compared with HDDs, we're looking at improved read and write performance. However, compared with write intensive [SLC and MLC flash] drives, we're talking about lower cost per GB, but with slightly lower write performance,” he added.

Dell said its price per GB in SC 4020 arrays could be as low as $1.66 per GB for flash and $0.58 per GB in hybrid flash arrays.

According to Dell, the move to TLC drives – which come in capacities of up to 3.8TB – has allowed it to double SC series storage array flash density, with up to 90TB of raw flash capacity per 2U of rack space.

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It also said it can offer the industry's lowest cost per gigabyte for all-flash arrays, with a 24x performance improvement and the same price per drive as 15,000rpm HDDs.  

The move means Dell SC series arrays – the enterprise SC8000, midrange SC4020 and entry-level SCv2000 – can be all-flash and populated with one or a mix of SLC, MLC and TLC flash or can be hybrid with flash and SAS spinning disk.

All flash storage sees data is stored in cells by electrical switching between states 1 and 0. In SLC (single level cell) flash there is only one switch and two states – 1 or 0.

In MLC (multi-level cell), two switches per cell provide four possible states, and in TLC (triple level cell) there are three states, which increases the amount of data one cell can hold to eight possibilities.

The downside to increasing numbers of 1/0 states per cell is that writing to flash is not just a simple overwrite operation, but a process that requires copying into cache all data in a page or block made of many cells, updating it, erasing the existing block and replacing it with the updated information. This takes time, central processing unit cycles and contributes to wear in the flash chip.

Read more on Flash storage and solid-state drives (SSDs)