Sandisk: vRPM and LDE

More active on the SSD market in terms of communiqués than products, Sandisk has put forward two propositions that look to standardize somewhat the situation with respect to SSDs.

The LDE, standing for Longterm Data Endurance, aims to stanardize figures in terms of SSD lifespans. Based on a standard usage of the SSD, it will be expressed in terabytes and will represent the amount of data that can be written on an SSD over its lifespan. Sandisk has offered the LDE to JEDEC, but the concept still has not been adopted, what is considered to be a standard load is still to be defined and the programme needed to reproduce such a load so as to measure the LDE, still has to be written. There is no guarantee, then, that Sandisk will manage to get the industry to accept the LDE, though without any doubt it would be a positive point if it does.

As for vRPM, standing for Virtual RPM, it is a measurement supposed to give us all a means of comparing SSD performance to hard disk performance, Sandisk working on the principal that it is this that is used to compare HDDs one to another. This is true, but comparing HDDs by comparing RPM has never been very accurate and to continue along this road does not seem a particularly clever idea.

Anyway, to calculate this vRPM, you have to calculate, for a usage constituting 50% reads and 50% writes, the average number of I/Os per second. This figure is then multiplied by 50, and hey presto, you get your vRPM. Using the same concept, we learn that our Western Caviar SE 16 640 GB has a vRPM of 4145 without NCQ, 8330 with, and that the VelociRaptor is at 7530 without, and 17790 with. C’est magnifique!