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rand_x0r

Member

Registered: 2014-04-22

Posts: 17

SSD Overprovisioning questions

Hello,

I've read alot about it(overprovisioning - lets call it OP). But so far I can't get a confirmation about some stuff.

In one article it was written that only recently SSD vendors have allowed the user to use all the space on his drive, thus disabling the OP.

Hence I was wondering - how much space is reserved for OP(by default)?

Now many of the SSD disks are 120 GB or 128 GB(also 240GB vs 250+GB), so I was wondering(may sound like a dumb question):

Are the 120 GB the same just that those 8 GB are used for OP?

Now, I've also read that Samsung have a tool for overprovisioning - which is Windows only.(but my current drive is not from them)

What is the difference between just not formatting some space on the SSD or using the tools provided by the Manifacturer?

It seems that SSD's use the blocks that are not marked as used(or have been used and then discarded) for OP - is that correct?

Hence if discard is enabled on ext4 - shouldn't the SSD use the freespace even if it's formatted?

Also is it important to have continous OP space since SSD don't need blocks to be sequentially ordered?

I've also found a tool called blkdiscard that basically discards on the block level, but hdparm has the secure erase option which seems to do the same - just with the whole SSD.
Is that correct or am I missing something?

And what's the point in using Host Protected Area?

I currently have a used and formatted 120 GB SSD(all of it is formatted, but I don't need the data on it), so I am wondering -

Do I need to secure erase it and then use the Host Protected Area OR should I just reformat it, leaving a big unused chunk at the end of it and blkdiscard the unformatted chunk?
Or maybe, just maybe since it's not a new model - it has an big OP space that is just hidden(My question about the 120 GB vs 128 GB).

Thanks for any answers.

Last edited by rand_x0r (2015-03-13 16:21:25)

tursas

Member

Registered: 2013-02-20

Posts: 4

Re: SSD Overprovisioning questions

I don't know what overprovisioning is, but the size mismatch you're seeing (120GB on a 128GB drive) is because of the difference between GiB and GB. Disks are usually labelled with their size in GB (= 1000000000 bytes) while computers report in GiB (= 1073741824 bytes). The difference is negligible in small drives, but noticable when you get to bigger sizes: 128GB = 120GiB, 1000GB ("terabyte") = 931GiB, etc.

karol

Archivist

Registered: 2009-05-06

Posts: 25,440

Re: SSD Overprovisioning questions

I don't know what overprovisioning is

You can just Google it :-)

http://www.anandtech.com/show/8747/sams … evo-review

As for the Wear Leveling Count, it might actually be taking into account that a fixed portion of the installed NAND is used in SLC mode for the TurboWrite buffer. The 120GB model has 128GiB of NAND, of which 9 GiB are used for 3 GiB TurboWrite Buffer, so that makes 119 GiB of TLC capacity for both overprovisioning and user addressable space.

By the way, this also implies that because of TurboWrite these Samsung EVO SSDs (including the previous 840 EVO) have less overprovisioning space than most other SSDs.

frostschutz

Member

Registered: 2013-11-15

Posts: 1,419

Re: SSD Overprovisioning questions

Are the 120 GB the same just that those 8 GB are used for OP?

I think that's usually the case...

What is the difference between just not formatting some space on the SSD or using the tools provided by the Manifacturer?

None, provided the unpartitioned part really was never ever in use. If it was you'll have to create a partition on it and blkdiscard.

Hence if discard is enabled on ext4 - shouldn't the SSD use the freespace even if it's formatted?

Sure.

In general you don't need overprovisioning at all. Just stick to whatever the defaults of your SSD are and use it normally.

Last edited by frostschutz (2015-03-14 12:20:38)

Alad

Wiki Admin/IRC Op

From: Bagelstan

Registered: 2014-05-04

Posts: 2,412

Website

Re: SSD Overprovisioning questions

Making all text bold defeats the purpose.

On topic, there's a disputed section on the wiki:

https://wiki.archlinux.org/index.php/So … iderations

Last edited by Alad (2015-03-14 14:34:51)

---

Mods are just community members who have the occasionally necessary option to move threads around and edit posts. -- Trilby

rand_x0r

Member

Registered: 2014-04-22

Posts: 17

Re: SSD Overprovisioning questions

So, I've read some more stuff and found out the following:

1. The ATA erase should behave like a full blkdiscard.(dependent on manifacturer's implementation).
2. HPA(Host protected area) tries to hide a portition of the disk from kernel, but there's a param that disables it and also it looks like it's bios dependent
Still, I can't really see, what's the point? Hiding the space so you don't "accidentally format and use it"?

Now about the advertised space - I've read that some people say that different RAID configurations are being used internally, hence those 8GB could be:
1. for parity.
But then again - some say they are used for
2. OP/buffers/etc.
Or it might be that vendors are advertising different sizes as stated by tursas
3. GiB vs GB

Now to ask some questions - should the OP space be formatted as a partition? And then blkdiscarded?
Or should I just blkdiscard it, without doing so?(That is - leaving it unformatted).

I know that formatting is all about modifying a GPT/DOS table but I don't know if maybe the SSD controller
uses that information to decide if a space is unused.

Also since

As for the Wear Leveling Count, it might actually be taking into account that a fixed portion of the installed NAND is used in SLC mode for the TurboWrite buffer. The 120GB model has 128GiB of NAND, of which 9 GiB are used for 3 GiB TurboWrite Buffer, so that makes 119 GiB of TLC capacity for both overprovisioning and user addressable space.

    By the way, this also implies that because of TurboWrite these Samsung EVO SSDs (including the previous 840 EVO) have less overprovisioning space than most other SSDs.

Does that imply the need for an OP partition?
Or if the answer above by frostschutz is correct(SSD use the freespace even if it's formatted).
What's the point in manual OP(leaving a huge empty partition)?

Also if LVM+LUKS are used but with TRIM enabled, does it matter to the SSD?
(since it will still know which blocks are free even if not what's that actual information, so worst case some info about usage patters might be revealed from a security standpoint of view)