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Re: Measuring (or calculating) how many bytes are actually written to disk when I repeatedly save a file

On Monday, April 08, 2019 09:41:10 AM Alexander V. Makartsev wrote:

> There are NVMe drives and SSDs intended to be used in servers with high

> workloads like cache storage. These server grade drives must be rated

> for at least 3 DWPD (Drive Writes Per Day) or more.


Thanks! I really hadn't encountered the acronym NVMe before.


Looking at some (e.g., by description "SAMSUNG 970 PRO M.2 2280 512GB PCIe Gen3. X4, NVMe 1.3 64L V-NAND 2-bit MLC Internal Solid State Drive (SSD) MZ-V7P512BW") seem to be the older style of SSD technology (V-NAND 2-bit MLC) which might be a little more reliable (though more expensive), than


some others which use the 3-D NAND technology, which presumably has about the same longevity / reliability as devices labeled as SSDs which use the 3-D NAND technology -- so I guess I have to be careful in how I shop (which is always the case, anyway).


Two links, both in the same ballpark pricewise:


* [[https://www.newegg.com/Product/Product.aspx?Item=N82E16820147693][SAMSUNG 970 PRO M.2 2280 512GB PCIe Gen3. X4, NVMe 1.3 64L V-NAND 2-bit MLC Internal Solid State Drive (SSD) MZ-V7P512BW]]


* [[https://www.amazon.com/BLACK-SN750-NVMe-Internal-Gaming/dp/B07M64QXMN?tag=pcworld02-20&psc=1&ascsubtag=US-001-2899351-000-1442373-web-20][WD BLACK SN750 1TB NVMe Internal Gaming SSD - Gen3 PCIe, M.2 2280, 3D NAND - WDS100T3X0C]]


And thanks for the explanation / clarification on some of the terminology:


> This means, if you have a 500GB SSD rated for 3 DWPD and it has 5 year

> warranty, then you can safely write 1,5TB to it each day for next 5 years.

> That is 3 * 500 * ( 365 * 5 ) / 1000 = 2737TB in total. (TBW)


> You can convert TBW to DWPD if you want.

> Let's say we have 240GB SSD rated for 768 TBW and it has 5 year warranty.

> That will be ( 768 * 1000 ) / ( 365 * 5 ) = 420GB could be written per

> day, or 420 / 240 = 1,75 DWPD


> Let's say we have 256GB SSD rated for 300TBW and it has 5 year warranty.

> That will be ( 300 * 1000 ) / 1825 = 164GB could be written per day, or

> 164 / 256 =  0,64 DWPD


> IMO, an average consumer grade SSD (preferably MLC NAND based, 240GB+, 5

> year warranty) should be rated at least 1 DWPD to be worth buying, so it

> could be used (without paying constant attention to it,

> implementing various tricks and restrictions to its workload, etc) for a

> very long period of time, extending far beyond its warranty period, if

> your workload is lower than 1 DWPD.

> However, in reality it is so much trouble just to find suitable device.

> This involves browsing through terribly designed manufacturer websites

> with dark marketing patterns [1] and a pile of specification datasheet

> files.

> Also keeping in mind how SSD manufacturers don't like to talk about this

> inconvenient topic for them, trying to hide TBW DWPD ratings by using

> MTBF ratings instead.




> [1] https://darkpatterns.org/