Author Topic: Does anyone make good SSDs any more?  (Read 11830 times)

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Offline PlainName

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Re: Does anyone make good SSDs any more?
« Reply #100 on: May 19, 2024, 09:38:45 pm »
Doesn't wear leveling achieve that? Use half your disk and you've doubled the cells available for endurance.
 

Online mariush

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Re: Does anyone make good SSDs any more?
« Reply #101 on: May 19, 2024, 10:06:37 pm »
It depends on the controller

Some can switch the whole free space to pseudo-SLC and only convert to TLC or QLC when nearly all buffer is full. 

Some controllers have a dynamic or static + dynamic portion, up to a percentage of drive's space ... for example some older WD drives like SN570 had a maximum of 12 GB pseudo-slc write cache. Some samsung drives have a guaranteed 6 GB fixed (always there) + up to something like 150-250 GB for every 1 TB or 2 TB of TLC memory.
 
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Offline David Hess

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Re: Does anyone make good SSDs any more?
« Reply #102 on: May 19, 2024, 10:34:05 pm »
Doesn't wear leveling achieve that? Use half your disk and you've doubled the cells available for endurance.

It is not about using less of the drive; all of the cells are available for endurance.  Larger drives have greater total endurance because they have more cells available for wear leveling, and that is one way to get longer operating life, but of course it comes at the cost of buying a drive with more storage.

Drive endurance is proportional to size, but how many bits are stored per cell has an even greater effect, so a drive with the same number of cells but fewer bits per cell should have higher endurance despite lower capacity.
 

Offline PlainName

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Re: Does anyone make good SSDs any more?
« Reply #103 on: May 20, 2024, 07:38:17 am »
but of course it comes at the cost of buying a drive with more storage.

Yes, exactly. The question was why don't they sell smaller drives with longer life (due to SLC vs QLC), and my contention was that you might achieve the same thing from just buying a bigger drive and not using some of it, even if it has to be a huge drive in comparison - same usable size, same lifetime, just a different way to get there.

Edit: Of course, that's predicated on unused space being usable for wear leveling (which apparently may not be the case) and wear leveling actually not losing data. But it's a mature technology and cheap as chips, now :)
« Last Edit: May 20, 2024, 07:44:26 am by PlainName »
 

Offline David Hess

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Re: Does anyone make good SSDs any more?
« Reply #104 on: May 20, 2024, 02:21:25 pm »
but of course it comes at the cost of buying a drive with more storage.

Yes, exactly. The question was why don't they sell smaller drives with longer life (due to SLC vs QLC), and my contention was that you might achieve the same thing from just buying a bigger drive and not using some of it, even if it has to be a huge drive in comparison - same usable size, same lifetime, just a different way to get there.

I suspect it just comes down to economics.  There is not enough demand for longer endurance storage to support mass production of SLC drives at a cost competitive with TLC drives, even though this should be more cost efficient where higher endurance is required.  Commercial and consumer grade customers can just buy larger drives to satisfy their longer endurance needs.  More critical customers can pay the high cost premium of true SLC drives, although some companies like Tesla have screwed this up.

Quote
Edit: Of course, that's predicated on unused space being usable for wear leveling (which apparently may not be the case) and wear leveling actually not losing data. But it's a mature technology and cheap as chips, now :)

A good SSD wear levels across the entire drive even if only part of the storage is in use, and should be performing scrub on read and idle time scrubbing to prevent data loss.
 

Offline aqarwaen

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Re: Does anyone make good SSDs any more?
« Reply #105 on: May 21, 2024, 07:13:23 pm »
i bit off topic here.but i got question let say i bought new ssd then write enough it reallocate sectors on flash.then swapped memories.
so my question is in this case would ssd/controller able to detect that i swapped memories.would it still keep or remove bad sectors if i did such thing?
 

Offline ejeffrey

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Re: Does anyone make good SSDs any more?
« Reply #106 on: May 21, 2024, 09:52:44 pm »
The manufacturers should provide a way to reformat TLC or QLC as MLC or SLC, for those who want to trade off capacity for more endurance.

My understanding is that MLC isn't a lot better than TLC.  So you would need to be going to pSLC to get a real benefit, and few people actually want to give up 66% of their storage.  So unfortunately we are stuck with the situation where only way to get SLC/pSLC drives is to get "industrial" SSDs that are insanely over priced and under performing.

MLC is basically in a weird untenable position for most use cases.  If you have MLC, it's generally better for performance to split the same total capacity into TLC and pSLC.  It's only where you need a specific high sustained write performance, and you don't benefit from often being able to burst faster than that.  There are applications like this, such as DVRs, data aquisition, and network capture systems.  However, they are exactly the applications where they also value high capacity.  In that case, just distributing the data across multiple TLC drives can get you the performance you need at a much lower cost/GB.
 

Offline amyk

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Re: Does anyone make good SSDs any more?
« Reply #107 on: May 30, 2024, 01:43:43 pm »
The manufacturers should provide a way to reformat TLC or QLC as MLC or SLC, for those who want to trade off capacity for more endurance.
They actually do, but are quite secretive about it. I just came across this:


i bit off topic here.but i got question let say i bought new ssd then write enough it reallocate sectors on flash.then swapped memories.
so my question is in this case would ssd/controller able to detect that i swapped memories.would it still keep or remove bad sectors if i did such thing?
That probably wouldn't work since they tend to store the firmware there too. But otherwise the FTL structure are stored in the flash, so if you reformat it using the manufacturer tool it'll rescan and establish new bad blocks.
 


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