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    Hello thank you for your reply. there are many feature in linux that you might find it strange but they exist. I have manually created dm snapshot on ram but the performance of dm and loop device doesnt seem satisfactory to me and there is huge hit on them so i am trying to find a way to improve its performance. Commented Mar 5, 2022 at 10:49
  • I believed I showed you a way in my answer. (what is strange is not the feature, strange is how you use it!) Commented Mar 5, 2022 at 11:03
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    yes thank you. but the 50%-70% drop in practical situation is too much. is there any way to make read from loop device(not loop file as does --direct-io in losetup) direct? Commented Mar 5, 2022 at 11:13
  • I explained exactly that in my answer: my answer is multiple times faster than what you are doing, not 50% slower. and there's no such thing as "loop file", you're mixing something up! (dd on the ram disk really is a bad benchmark, see my explanation about context switches) Commented Mar 5, 2022 at 11:14
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    You just need to run the sudo modprobe… comment, and use /dev/ram0 in your md setup. Commented Mar 5, 2022 at 11:16