It's not so much the density of the SSD that's the issue, but specifically the Flash type used to get the density. MLC is cheap, but SLC is faster and lasts 10x as long.
Random quote from the internets that explains MLC and SLC.
MLC vs SLC head to headVendors may prefer not to discuss the differences between the technologies, but understanding the underlying technology can influence deployment strategies. So, what are the key differences between MLC and SLC flash SSD?
All flash memory suffers from wear, which occurs because erasing or programming a cell subjects it to wear due to the voltage applied. Each time this happens, a charge is trapped in the transistor's gate dielectric and causes a permanent shift in the cell's characteristics, which, after a number of cycles, manifests as a failed cell.
SLC uses a single cell to store one bit of data. MLC memory is more complex and can interpret four digital states from a signal stored in a single cell. This makes it denser for a given area and so cheaper to produce, but it wears out faster.
So, an MLC cell is typically rated at 10,000 erase/write cycles, while an SLC cell might last 10 times that before failing. However, manufacturers of products consisting of MLC cells can and do have ameliorating technologies and techniques at their disposal.
According to Andrew Buss, service director at analyst firm Freeform Dynamics, amelioration techniques used by most vendors include wear-levelling, which moves write cycles around the chip so that cells wear evenly; on-device deduplication, which reduces the volumes of data written and so lowers wear; redundancy, which reserves a portion of the device's capacity to replace cells as they fail; and write optimisation, which stores data writes so they can be made in large chunks to reduce the number of write operations. The emerging term for MLC products that incorporate such techniques is enterprise MLC, or eMLC.
Most such techniques are implemented in the device controller -- the interface between device and computer -- with companies such as
SandForce and
Intel among the most advanced in implementing such techniques, according to Buss. *
And despite the endurance issues related to SSDs, they remain, say vendors, more reliable than spinning media.
*Emphasis added by me.
Something not mentioned above, but hinted at if you read the amelioration techniques, is that you should NOT defrag an SSD. 1) You gain nothing in RW speed by defragging an SSD, it's running at the speed of flash RAM regardless. 2) You're reducing the life of the cells by needlessly moving files around. 3) Wear levelling (always writing to fresh areas rather than over-writing original data) means that fragmentation will occur very quickly on regularly changing files, but it doesn't matter as random access speed of flash RAM is effectively the same as serial access speed. Unlike with a spinning disk.