SSD. Why 480 not 500?

Why is it I used to get 500G SSD’s and now they all seem to be 480 or so?” – well I am glad you asked to. As I did.

For that matter – the obscure 500 as opposed to 512 when you know its going to be chips in classic 8, 16, 32, 64, and 128 chips.

Having had over provision and garbage collection cited as the reason – I was like “well isn’t that all dealt with by what used to be DISCARD passed to the OS for that drive / partition in fstab?” allowing TRIM to function where supported  (I believe you no longer have to inform newer kernels it figures it out – yay) …. well yes … but that assumes it is being presented as a drive, and not a virtual device as will occur in just about any enterprise environment. In short, if a RAID card is in the way – all bets are off.

I found this rather fantastic selection of articles apparently written by a chap called Les Tokar. While they are old now (dated 2011) there is MUCH to learn here. Nicely done that man. Chapeau.

  1. BENEFITS OF A SOLID STATE DRIVE – AN SSD PRIMER
  2. SSD COMPONENTS AND MAKE UP – AN SSD PRIMER
  3. SSD TYPES AND FORM FACTORS – AN SSD PRIMER
  4. SSD ADVERTISED PERFORMANCE – AN SSD PRIMER
  5. SSD MIGRATION OR FRESH INSTALL – AN SSD PRIMER
  6. GC AND TRIM IN SSDS EXPLAINED – AN SSD PRIMER

I feel enlightened. There were a bunch of mechanics there I was not up to speed with. Nicely done.

“SandForce Driven” SSDs can easily be spotted as their drive capacity goes against the grain.  Whereas we spoke of capacities of 32, 64, 128, 256 and 512GB above, companies that utilize SandForce SSDs have their product advertised in capacities that are typically 30, 60, 120, 240, and 480GB.  This is because SandForce is able to improve the performance and lifespan of their product through their firmware and over provisioning, over provisioning which typically steals away 7% of NAND flash memory for the consumer and as high as 28% for enterprise.

— Componentry / Over Provisioning.

So in answer – the over provision varies – however there you have it. You are getting more, but its not going to slow down as it fills, and will last longer in an environment without TRIM support.

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