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

• Date: Mon, 8 Apr 2019 18:41:10 +0500
• From: "Alexander V. Makartsev" <avbetev@xxxxxxxxx>
• Subject: Re: Measuring (or calculating) how many bytes are actually written to disk when I repeatedly save a file

 On 08.04.2019 17:39, rhkramer@xxxxxxxxx wrote: ```On Monday, April 08, 2019 03:40:54 AM Curt wrote: ``` ```Maybe an SSD is not the most appropriate storage device for frequent editing of large files. ``` ```That is what I'm trying to decide / determine. ``` 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. 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/ ```-- With kindest regards, Alexander. ⢀⣴⠾⠻⢶⣦⠀ ⣾⠁⢠⠒⠀⣿⡁ Debian - The universal operating system ⢿⡄⠘⠷⠚⠋⠀ https://www.debian.org ⠈⠳⣄⠀⠀⠀⠀ ```

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