Flash memory is opening a second front in its war on entrenched storage technologies. So far disks have been taking the heat, but DRAM is the next target.

The unannounced Sun F5100 product uses 80 48 GB flash SO-DIMMs to create a 4 TB cache appliance. Cool.

But once the SO-DIMMs are on the market vendors will want to put them in notebooks. The question: will they displace more disks or DRAM?

Isn’t “enhance” nicer than “replace?”
The flash DIMMs are accessed as disk drives through a thin driver, which makes them fast. As a disk look-alike they aren’t a direct replacement for RAM. But a 2 or 4 GB SO-DIMM DRAM is plenty for most folks.

If a flash DIMM is configured as the boot device users will get most of the advantages of a more expensive SSD in a smaller and cheaper package. For many users 48 GB of main capacity is plenty, making a disk optional.

Also, flash is a lot cheaper than DRAM. 4 GB notebook SO-DIMMs have just come to market priced at over $100 per gigabyte. How the flash SO-DIMMs will be priced is still a mystery, but since the memory chips typically are over 90% of the cost of a DIMM, a 48 GB SO-DIMM should be less than $200.

Expensive compared to a disk drive, cheap compared to DRAM. But not cheap enough for netbooks.

Peaceful coexistence?
In 2 years notebook vendors could be offering a scaled-down version of the traditional enterprise tiered storage architecture: high-speed DRAM; fast SO-DIMM for booting, application and scratch storage; and a large capacity hard drive for bulk storage. Faster performance, more capacity, lower power consumption and cooler notebooks. It could be good.

However, as the bootable SD card slot in the new MacBooks shows, there is more than one way to get flash into a system. Some of us would like to be able to easily swap out boot drives on as the cards, but most of us will prefer to have our boot drive inside the notebook where it won’t can’t get lost. SB cards will also continue to have a significant cost advantage over flash SO-DIMMs due to high volume.

The Storage Bits take
None of the players are standing still. In 12 to 18 months that 48 GB flash DIMM will be 96 GB or more. The current high price for the 4 GB SO-DIMM will drop to reasonable levels. And drive vendors will be offering 1.5 TB 2.5 inch drives.

Of course, we don’t know how well the new flash DIMMs will perform. Much depends on the quality of their embedded flash controllers, which often isn’t too good in first-generation designs.

Flash DIMMs will take a piece out of both the DRAM and disk markets, but how much of each remains to be seen. As usual, it is a dogfight in the storage business, and this on could get really nasty.

Here’s a thought: how about a 50GB notebook with 1 TB disk? Technically, 48 GB is flash, but since it is on an SO-DIMM and most consumers don’t know the difference between DRAM and disk, let alone flash, is it really that wrong? If it is defensible, expect storage marketers to do it.

If I were Fusion-io, I’d be looking into the flash DIMM business. Know them, they already have.

Comments welcome, of course. I worked in Sun’s storage group for 3 years in the mid-90s. I’ve done work for Fusion-io in the last couple of years.