NVME performance degradation?

[Barnash]

So a few months ago I got myself the Sabrent Rocket NVME 1TB and was very pleased with it's performance.

Out of curiosity, after I freed it up from almost full 80%, I ran a bench today and surprisingly there's a big difference specially in write speeds.

 

Is this normal?

Could be that it's run out of dram and needs to purge that first?
Might it be related to benching right after freeing up data?
Like as if the sectors are not truly free yet for some weird reason?

As far as I understand when you remove files or move them it doesn't actually free the sectors but unlocks them for allocation for new data to be written.
but it doesn't actually make sense because if it were true you basically get only one time use of 3k speeds up until the point the entire sectors been used once and since then you're limited to only already used "unlocked" sectors at 1k speeds.
same logic for dram?

 

 

Here's the bench of day-one after a fresh OS install, Aug 23rd

 

 

And here's today

 

 

[Juular]

Quote

Out of curiosity, after I freed it up from almost full 80%, I ran a bench today and surprisingly there's a big difference specially in write speeds.

 

Is this normal?

Short answer - yes. For some other drives write speeds may drop to as low as 100 MB\s (QLC SSDs like Intel 660p and Crucial P1), for most other drives it's around 400-500 MB\s. Try to update firmware on it, it may help to raise write speed.

 

Long answer, it's because multi-bit NAND cells are the slower to write the more bits per cell are there (three in that case with TLC NAND). SSD controller mitigates slow native write speeds by caching data on DRAM (either on-PCB on in system RAM) and temporarily writing a new data in SLC\MLC mode (1-bit & 2-bit) if there's free space for that, the less free space are available the less is that buffer in size. So with almost full SSD you'll get write speed degradation after less data written in one go than with empty one.

 

Overall that's very good SSD, with good write speeds and caching, don't worry about that, it's just how it works.

 

As of removing unused, deleted blocks, the SSD and OS (assuming it's WIndows 10) do that automatically (it's called TRIM).

[redbread123]

wow you must be good at nvme, you have 1797 hours...

[Juular]

1 minute ago, redbread123 said:

wow you must be good at nvme, you have 1797 hours...

That's only about 2-6 months of usage.

[redbread123]

Just now, Juular said:

That's only about 2-6 months of usage.

r/woosh? in a game thats a lot of hours

 

[Barnash]

17 minutes ago, Juular said:

Overall that's very good SSD, with good write speeds and caching, don't worry about that, it's just how it works.

Well, first of all thanks for the clarification. I'm not worried anymore.

Quote

So with almost full SSD you'll get write speed degradation after less data written in one go than with empty one.

I'm finding it hard to wrap my head around it.
But I freed up the space so it's not full anymore, shouldn't it reset?
What if I'll get more RAM? Will It effect degradation?

So I assume the first time 3K write speeds were thanks to an empty dram basically?
It was measuring dram speeds?

[Juular]

3 minutes ago, Barnash said:

Well, first of all thanks for the clarification. I'm not worried anymore.

I'm finding it hard to wrap my head around it.
But I freed up the space so it's not full anymore, shouldn't it reset?
What if I'll get more RAM? Will It effect degradation?

It needs some time for garbage collection to kick in. Are you on OS Windows 10 ?

 

No, more RAM will not improve anything, this SSD doesn't use host caching, it has on-board DRAM cache.

[porina]

Try running the Windows "Defragment and optimise drives" app. Make sure the drive is listed in there as a SSD, and if so, hit Optimise. This forces it to do a TRIM. While it should normally issue a TRIM on every file deletion, if the drive is busy it might skip it. This will force a run on the whole free area.

 

I'm not sure on the next part. I don't think the drive has to actually perform the TRIM immediately on issuing that command. You might or might not see a performance increase at that point, or might have to wait a bit if the drive decides to do it slower in the background.

[Barnash]

3 minutes ago, Juular said:

It needs some time for garbage collection to kick in. Are you on OS Windows 10 ?

 

No, more RAM will not improve anything, this SSD doesn't use host caching, it has on-board DRAM cache.

Yes, Windows 10

So I assume the first time 3K write speeds were thanks to an empty dram basically?
It was measuring dram speeds?

[Juular]

1 minute ago, Barnash said:

Yes, Windows 10

So I assume the first time 3K write speeds were thanks to an empty dram basically?
It was measuring dram speeds?

Empty NAND, the very storage where's your data are being written at. For long term storage it's written in 3-bit mode (slow), for temporary caching it's written in 1-bit mode (fast) so the less there's empty space to cache on the less data you can write in one go without performance degradation. After some time it'll empty that temporary cache and you can write a bit less amount again, down to the size of onboard DRAM (1GB usually for 1TB drive) when it's completely full.

[Sakkura]

33 minutes ago, Barnash said:

Could be that it's run out of dram and needs to purge that first?

Might it be related to benching right after freeing up data?
Like as if the sectors are not truly free yet for some weird reason?

As far as I understand when you remove files or move them it doesn't actually free the sectors but unlocks them for allocation for new data to be written.
but it doesn't actually make sense because if it were true you basically get only one time use of 3k speeds up until the point the entire sectors been used once and since then you're limited to only already used "unlocked" sectors at 1k speeds.
same logic for dram?

The DRAM doesn't store data, it's just a temporary buffer and more importantly holds the FTL data. It's not about the DRAM.

 

When you erase data on an SSD, it doesn't get erased. It just gets marked as ready for deletion. Then it's up to the garbage collection implementation to clean it up whenever it's convenient. If you've just erased a lot of data, that can temporarily slow down the SSD's performance afterwards.

 

DRAM is volatile and has way lower latency, so these kinds of issues aren't relevant.

[Barnash]

1 minute ago, Juular said:

Empty NAND, the very storage where's your data are being written at. For long term storage it's written in 3-bit mode (slow), for temporary caching it's written in 1-bit mode (fast) so the less there's empty space to cache on the less data you can write in one go without performance degradation. After some time it'll empty that temporary cache and you can write a bit less amount again, down to the size of onboard DRAM (1GB usually for 1TB drive) when it's completely full.

I see now, so it's kind of a buffer principle.

Thanks man, I'm blown away from how helpful you are.

[Sakkura]

2 minutes ago, Juular said:

Empty NAND, the very storage where's your data are being written at. For long term storage it's written in 3-bit mode (slow), for temporary caching it's written in 1-bit mode (fast) so the less there's empty space to cache on the less data you can write in one go without performance degradation. After some time it'll empty that temporary cache and you can write a bit less amount again, down to the size of onboard DRAM (1GB usually for 1TB drive) when it's completely full.

A normal SSD is never completely full, as some of the flash is set aside. You're never down to just the DRAM.

[Barnash]

12 minutes ago, porina said:

Try running the Windows "Defragment and optimise drives" app. Make sure the drive is listed in there as a SSD, and if so, hit Optimise. This forces it to do a TRIM.

 

31 minutes ago, Juular said:

As of removing unused, deleted blocks, the SSD and OS (assuming it's WIndows 10) do that automatically (it's called TRIM).

Guess what, that actually worked.

[Mark Kaine]

7 hours ago, Barnash said:

 

Guess what, that actually worked.

Wow,  lol, good... I was already worried the degradation of these drives after only 6 months is normal... 

 

I do TRIM like once a week or so btw,  supposedly Windows does this automatically but I've turned that off,  it also might be a bit buggy so it doesn't do it always when it's supposed to, not sure. 

 

 

Also same spiel for standard hard-drives if you have them,  need to defrag them every few weeks or so - if windows doesn't automatically.