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I am using LUKS over RAID0. I have executed cryptsetup -v --cipher aes-xts-plain64 --key-size 512 --hash sha256 --iter-time 2000 --use-urandom --verify-passphrase luksFormat /dev/md0

Everything shows me that the partition is LUKS protected /dev/mapper/raid0luks is active

When I am writing on this partition, it is fast, so I wanted to monitor the overall process. TOP shows me the dmcrypt_write process 20% CPU usage, whereas iotop shows 0 bytes written on dmcrypt_write line.

I would like to be sure I am not missing something due to good write performances. Thank you for your tips.

akira2x3x
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1 Answers1

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This is expected. I haven't looked into it too deeply, but I would assume that dmcrypt_write is writing at a lower level than where the statistics happen.

Good performance should be expected on any CPU supporting the AES-NI instruction set, dmcrypt_write never goes higher than 2% CPU usage for me when writing around 185 MiB/s. Performance testing with openssl gives me around 1.8 GiB/s for AES-256 in CTR mode.

AndrolGenhald
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  • Thank you. I will try to investigate more and post update on that topic. I can clearly see CPU usage on dmcrypt with tool like atop : 20% every 1s. Moreover, it indicates write ope on LVM which in my case is associated to /dev/mapper, write ope on RAID0 (layer under), write ope with ftpd (client write ope) BUT dmcrypt_write is 20% CPU and no write ope – akira2x3x Jul 03 '18 at 08:41