I’m new to forum but i’m a bit too old in PC’s from the hard days of 80’s (Sinclair spectrum, oracle, first apple’s, commodore’s Amiga this is still working excellent etc.) of 512MB soft didks.

A little question, what’s the percentage number of over-provisioning for Sandisk Extreme Pro. And if for consumers  is (for example) 7%-10% in 480Gb (the size of 480 model), 7%-10% in format size (i think 447Gb) or 7%-10% in 512Gb (total amount of NAND’s in 480 model).

The 480Gb is the size of 512 when converted from gibibytes to gigabytes (1024/102/1024*1000*1000*1000).

I appreciate any answers or views.


all Sandisk drives and other manufacturers have spare blocks that can be used if some fails, for Sandisk there are 5-10% of the maximum capacity in order to keep the drive safe for a long time. For the extreme pro there are more blocks to spare and thats visible to the capacity of the drive also, thats why its counted so strange.

Of course you can let more space available for over provisioning if u left unallocated space to your drive that will then be used if 0on more spare blocks are left to replace.

Ok, understood, but lets speak with numbers. Samsung Evo 250GB when formated is about 233GB and in this number you can put the over-provisioning space, Samsung Pro 840 256GB is 238GB formatted and in this space you can set the over-provisioning. Samsung 840 Pro 512 is 476GB  formated and in this space you can set overprovisionig.

Samsung 512Pro and Sandisk Extreme Pro 480 have the same total amount of NAND’s 512 summary.

So, a Sandisk formated must be about 477GB but finally is 477Gb unformatted. The other space i think is the area of spare blocks. The difference between the 447GB (full formated without free space) and the 478GB who must be formatted is the over-provisioning space? or not?

I think Sandisk to prevent problems, special with a 10 years guarantee (as and other manufacturers) have make a replacement area with block’s who isn’t visible to end user.

I don’t know if this area is used as a spare blocks or to over-provisioning, overprovisioning and spare blocks are to total different things.

The over-provisioning procedure use TRIM commands and working through the OS. If the OS can’t find free space (unallocated-empty) in an ssd can’t  run the overprovisioning procedure properly. Overprovisioning (OP) procedure keep ssd’s run healthy, optimizes performance, extend lifespan.

Spare blocks is replacement blocks in an ssd.

I believe some more information from Sandisk are necessary.

And i don’t believe is counted strange, just count the total capacity if you leave the spare blocks.

So, anyone can tell for sure if this area of 30GB of invisible spare blocks are used for something else like the OP procedure?  

May be Sandisk can have some special commands for this invisible area, may be, but as anyone can see in some reviews if you leave a good OP area (unallocated space-non formatted about 20%) the performance increase and extend the lifespan of ssd.

And Deponia where you can see this blocks? Sandisk Extreme Pro 480 is 477GB unformatted and 447 formatted, you can imagine this blocks because the number of NAND’s and the conversion to GB’s. 512 total amount of NAND’s will be 480GB formated but is 447GB formated. 


Of course i know that the trim commands work with the spare blocks and determine where they are needed and so all the process of the replacement works. About the capacity the standard over provisioning that is made to the extreme pro is not visible to the end user so a 480 drive is basically a 512GB drive that has spare blocks for replacement. So they can reach the extended warranty for this drive.

This is what i understood from my research and i may be wrong.

Sorry, but OP and trim commands don’t work through “invisible” spare blocks, and Sandisk Extreme Pro isn’t 512GB is 512GiB’s (not GB) is just the total capacity of NAND’s when converted in GB’s  (from gibibytes to gigabytes (1024/102/1024*1000*1000*1000) as i wrote previously give you finally about 480GB.

The 500Gib’s (Samsung EVO etc.) gives you 465GB, and the 480Gib’s of Sandisk gives you 446GB.

As i know Sandisk doesn’t have 480GiB’s NAND but 512GiB’s, for this reason i believe the 32Gib are spare blocks of an invisible free space for nCache™ Pro Technology or just for spare “replacement” blocks or for both. This space i don’t think is for OP procedure and as i know till now W7 and W8 don’t have commands for invisible area’s, except if the Sandisk have some “special” commands in controller for this area of blocks.

I believe consumers must have better information, most company’s gives some help about OP and all the other techniques to prevent you from undone ssd’s.

Not anyone backup daily, not anyone have the same abilities or software to restore falling systems but anyone can have the necessary information to prevent bad situations or to run his PC smoothly. 

And finally the question remaining, OP or not OP and if yes what’s a good percentage number? in no why?

Answers like yes there is a space and for plus you can leave a bit more space isn’t i can say (sorry deponia) “professional”. Is a view (like me) of a member of a forum and i appreciate that. But i need information that has a base.

Sandisk any answer?


Sure im not a Sandisk engineer so i cannot provide you the exact technical details and as i previously mentioned its what i know from personal research.

In that case you want a detailed and professional answer you can contact the sandisk support directly and get clarity on the issue.

Here is a review of the EX Pro that may answer your question about user over provisioning (page 2):

SanDisk Extreme Pro Review

Factory and user over provisioning space are two different things. Consumer SSDs do not have much factory OP space in order to keep the price down.

Business/Enterprise oriented SSDs always have more factory OP space, generally that is ~50% of the specified user space of the SSD.

While a 512GB and 480GB SSD actually have the same amount of NAND (512GiB), the 30GB difference between the two is the difference in factory OP space, working in GB rather than GiB for this example.

Whether or not user OP space is truly useful depends on the way the user actually uses the SSD. Most of us never stress our SSDs in the way that review performs consistency testing with and without any extra user OP space.

I usually set aside ~15% of a SSD’s capacity as user OP space, but I cannot tell you if it really helps, given my usage profile.

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These are very interessting and helpful information, thank you very much.