SSD spare space confusion.

[IanWorthington]

Can someone help me understand this?

On many, though not all, SSDs, performance and life is said to be increased by not allowing the drive to become more than 70-75% full. It's said that this can be done either by just keeping an eye on the the space, or by doing a secure erase and leaving 25-30% unpartitioned.

These two things don't though seem the same to me: untouched space is not the same as unformatted space surely? Or does the drive controller know when something's only formatted and with no "real" data?

i

 

[postmortemIA]

controller knows where's data and how much of it is used. partitioning is only on logical level, more or less emulated to appear as same as old fashioned hard drives that have sectors and cylinders

 

[Brahmzy]

Do it right. Secure erase the drive, partition a 74%-80% partition and you're good.

 

[IanWorthington]

Thanks.

This machine will be running linux and I'll need hibernation support. Any thoughts on making that unused area the swap partition, mounted with discard?

i

 

[brandonmatic]

Is this recommendation based on the specific SSD controller that's used? Or does it more or less apply to all SSDs?

 

[mv2devnull]

controller knows where's data and how much of it is used. partitioning is only on logical level

True. It is the initialization of filesystem (aka "formatting") that can make the controller think that there is data. For example, NTFS offers "quick" and "other" formatting. IIRC, the quick writes only the metadata, but the other touches more of the logical sectors.

Another example -- less common with SSD and not about filesystems -- are the RAID modes, where initialization of an array does touch every sector of a partition in order to establish consistent state.


In other words: unused space within partition with a filesystem may or may not be unused as far as the drive controller knows. "Unpartitioned" part of disk is explicitly unused.

 

[Cerb]

EXT4 supports TRIM, with the discard mount option. So just mount with discard, and go on about your day, just like people running Windows 7+ do.

SSDs effectively start with all blank data. When data is written to, it's not blank. When it's deleted, it's still not blank, it's just not being pointed to anymore. TRIM goes and tells it that space can be blanked.

 

[Erva]

So just keeping an eye on the space may or may not achieve the desired result? It's best to make an unused partition?

 

[Brahmzy]

It is best to secure erase the SSD and create your initial partition only 80% of the available space. That way, that un partitioned 20% is forever "locked in" as OP space. If you let Windows install by default, it'll partition out the entire drive. And never low-level format an SSD. Always use the quick option.

And yes, some drives need more OP than others. Some (mainly newer drives) are coming with more built-in OP space unseen by the end-user. For example, an 840 Pro needs more OP than an 840 Evo, because Samsung has learned that write performance consistency can only be accomplished with more OP.

That said, I'd still give at least 20% to any SSD out there today. This will also make your drives last longer. The more OP (room), the better the SSD controller can perform its wear-leveling.

 

[Cerb]

And yes, some drives need more OP than others. Some (mainly newer drives) are coming with more built-in OP space unseen by the end-user. For example, an 840 Pro needs more OP than an 840 Evo, because Samsung has learned that write performance consistency can only be accomplished with more OP.

I think you have those mixed up. The Evos have more OP than the Pros.

But, the reasoning is solid, and the new Evos have pretty fair consistency, such that some people are choosing them instead of the Pro, even with the budget for a Pro (but, if the Pro has OP user-added, it also gets faster, so you can have your cake and eat it too). We're also seeing the same pseudo-SLC cache tricks used with Toshiba/Sandisk MLC, at least with the new Sandisks, if not others (I'm not sure if anyone knows for sure if the new Toshibas do that or not, FI). With faster-writing MLC and added OP, you're better off, but the real-world difference is going to be very small, and likely not noticeable.

Users that perform lots of I/O, or mostly random I/O, may look closer (and generally choose a Neutron, M500, or Extreme II, depending on their location and budget), but for 99% of everybody out there, it's not worth much worrying over. The major flash companies have, each in their own way, made their drives good enough, and improved them in the right ways over time, for ever-better actual performance, and good enough longevity to last through being handed down through multiple PCs.

Except for super heavy users, this should be typical of the differences between them:
http://www.tomshardware.com/reviews/samsung-840-evo-review-1tb-ssd,3567-11.html
(sorry AT, but I guess Tom's has better SEO for some of their articles )
Useful AT page:
http://www.anandtech.com/show/7173/...w-120gb-250gb-500gb-750gb-1tb-models-tested/6

The Evo needs that added OP to compete, but it's right up there with the Pro, at a lower cost, and offers more consistent performance with the factory/minimum OP. But, as you can see, all of the newer SSDs from major makers are, in normal use, awfully close to one another in performance, as well, so aside from making a point to purchase one by a solid maker (Samsung, Sandisk, Toshiba, Plextor/Lite-On, Intel, Crucial/Micron, and Corsair's Neutron, as an odd-one-out), there's much more worry than is justified; largely based on momentum, from the earlier 2008-2011 SSDs, many of which were craptastic in quite a few ways.

So just keeping an eye on the space may or may not achieve the desired result? It's best to make an unused partition?

Depends, If you have TRIM support, you generally don't need to worry about it. Also, it's not a life or death issue. SSDs that should have had more factory OP for desktop use will have better performance and use write cycles much slower, while SSD with sufficient factory OP will gain substantial performance, but not much in terms of reduced wear (and there's not an absolute best amount, either; how they implement wear-leveling is a factor, so one series w/ 7% might need more, while another with 7% might be fine w/o TRIM). Even with all that, most drives are going to last longer than the service life of their host PCs, by a significant margin.

 

[WhoBeDaPlaya]

I usually do a FW upgrade out of the box, secure erase, then leave a portion of it unpartitioned.
Left 25.76GB on the tail end of a Samsung 840.

 

[Brahmzy]

I think you have those mixed up. The Evos have more OP than the Pros.

I think you misunderstood my post. I know the Evo has more built-in OP. That's my point. It's a newer drive. Samsung learned their lesson with the Pro.

-Especially when sites like this specifically bench write performance consistency. Expect future Samsung drives to have the same or more OP than the Pro.

 

[Cerb]

I think you misunderstood my post. I know the Evo has more built-in OP. That's my point. It's a newer drive. Samsung learned their lesson with the Pro.

I wonder...

The 840 has the same amount of OP as the Evo (the 840 technically has more, actually), and both are TLC. I wouldn't put it past Samsung to do the exact same thing again, when they update their premium MLC line. It's hard to imagine they didn't know the 840 Pro was going to have a bit fragile performance (my guess is they figured since >95% of buyers wouldn't push it hard enough to tell, they didn't care, and the larger space worked well for marketing purposes...but I have been accused of being a cynic, before ).

 

[Brahmzy]

Hmm. I wasn't aware the vanilla 840 had the same OP as the Evo. There goes my theory.
Makes you wonder how bad the drives would run with the same OP as the Pros. Maybe pretty bad, which is why Sammy augmented their TLC stuff with more OP and figured the MLC Pros were 'good enough' with less. Who knows.
Any word on RAPID support for the Pros? I've got quite a few systems at home and work with single Pros. RAPID support would be a real cheap (free), easy upgrade without setting up fancy cache and or buying Primo etc. Activate n forget about it.