How do I measure the time taken for Samsung's Intelligent TurboWrite buffer to be empty again?

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I have a 1 TB Samsung 860 QVO SSD which is Samsung's QLC NAND SSD offering.

It has an SLC cache used as a buffer during writes and I observed speeds of upto 520 MB/s for up to 10 gigabytes of sequential data transfer before the write speed tanked to 75-80 MB/s.

I tried writing another file to the drive after idling for more than an hour but I'm still seeing 80 MB/s write speeds. I also rebooted my notebook although I'm not sure that helped with anything as write speeds are still 80 MB/s.

I should mention that I'm running Windows 10 and this drive is used for nothing but storing data. It's not the boot drive and it doesn't store the pagefile or hiberfil.

Is there a way for me to see how much of the buffer is utilized at any given point so I can only start transferring files when it's empty?

Vinayak

Posted 2019-05-21T17:25:11.020

Reputation: 9 310

Questions: (1) How old is the SSD? (2) Are you using SATA III interface? (3) Have you tried Samsung Magician, especially to check for driver update, and if you did, what were the results? (4) Are Write Cache and AHCI enabled?

– harrymc – 2019-05-24T07:12:00.597

@harrymc 1. The SSD is about 10 days old. 2. Yes, I'm using SATA III. 3. Samsung Magician didn't show a driver update for the SSD. 4. I'm not sure how I can check whether or not this is enabled. RAPID mode is disabled though. – Vinayak – 2019-05-24T07:24:42.180

@harrymc Here's the spec sheet. I have the 1 TB variant.

– Vinayak – 2019-05-24T07:30:04.377

Try all the other options of Samsung Magician - it's just about the only utility that can interface with a Samsung SSD. If nothing is useful, and as this is a new disk, you could ask Samsung Support. – harrymc – 2019-05-24T09:38:43.410

@harrymc it doesn't look like Magician has any provisions to check the available buffer size or to see how much of it is used up. I was wondering if there's any other way to get this info based on what we already know (i.e. the buffer size) and the disk usage – Vinayak – 2019-05-27T05:40:42.877

Answers

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You findings are exactly the same as of the anandtech review
The Samsung 860 QVO (1TB, 4TB) SSD Review.

In the section SLC Cache Sizes & Energy Consumption, it says:

The Samsung 860 QVOs run out of SLC cache right on schedule, at 42 GB for the 1TB model and 78 GB for the 4TB. After that, they are both slow and very steady for the rest of the test.

The 1TB 860 QVO falls below the sequential write speed of a 1TB hard drive once the SLC cache runs out, but the 4TB model is able to sustain twice the write speed and remains ahead of not just the hard drive's speed, but also some of the slower TLC drives.

enter image description here

First conclusion is that you may double the speed of the disk by trading your 1TB model for a 4TB, although this won't make it super-fast.

You may also gain some speed by enabling the Samsung Rapid Mode via the Samsung Magician application, which basically augments the size of the cache by dedicating it some RAM. For more information see the post Is it beneficial to enable Rapid Mode on a Samsung solid state drive? (where my answer is not that positive).

harrymc

Posted 2019-05-21T17:25:11.020

Reputation: 306 093

As a personal comment, I'm not in favor of an SSD that under load becomes slower than, or only as fast, as a spinning drive. – harrymc – 2019-05-24T11:21:18.363

The article says the drive has up to 42 gigs of intelligent TurboWrite buffer. Does that mean that for sequential transfers of up to 42 gigs, the buffer will be able to provide 520 MB/s speeds and then throttle it? If that's the case, I was wondering how long it would take to recover after this write operation since from what I observed, even after an hour I would only see 520 MB/s speeds for up to around 200-400 MBs and then it'd drop to 75-80 MB/s which is terrible IMO. – Vinayak – 2019-05-27T05:43:45.830

What you see is the speed of the connection computer-SSD. As the connection is much faster than the internal writing speed of the SSD, it goes at 520 MB/s as long as there is room in the buffer, but once full then data needs to be written out to the disk in order to receive more. This slow speed will continue as long as there is lots of data in the buffer. Evidently 520 MB/s is the connection speed and 75-80 MB/s is the writing speed, and it takes quite some time to empty the buffer. You don't have a fast SSD in there. – harrymc – 2019-05-27T06:31:08.473

I am well aware of that fact. What I mean is that I'd like to see the 520 MBps 'connection speed' when I'm using the SSD after I've given it enough time to recover from the sequential write operation. If I assume the worst and the SSD writes at even 50 MB/s, it should be able to complete writing all the data from the 42 gig buffer to disk in 14 minutes. So what I don't understand is how even after idling for 1 hour without using the disk can it still write at 75-80 MB/s and not 520 MB/s for at least 42 gigs of sequential data. – Vinayak – 2019-05-27T06:39:24.343

1I was hesitating to accuse the SSD of having a memory-management bug, but I must say that probably this is what happens, so buffer memory is lost and is reduced below 42 GB. What you can do is look for a firmware update or contact the manufacturer's Support. But if no improvement, I hope you can be reimbursed. – harrymc – 2019-05-27T06:45:00.547

Thanks. I think I'll try to get it replaced. The return window on this has closed but if this is a problem with other 860 QVOs as well, then maybe Amazon might make an exception and I'll replace it with an MX500 or an 860 EVO. – Vinayak – 2019-05-27T07:02:27.110

Asked: 2019-05-21T17:25:11.020

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Active: 2019-05-24T11:21:05.963