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When I try to use TrueCrypt or VeraCrypt, write speeds are very slow, but read speeds are fast. This happens with both programs, and it occurs regardless of whether I'm using an encrypted file container or an encrypted partition. (So, no, this isn't fragmentation etc.)
For example, on my SSD where unencrypted read and write speed both benchmark over 1GB/s on CrystalDiskMark, an encrypted volume using AES-XTS and HMAC-RIPEMD-160 benchmarks read speeds of 810 MB/s vs. write speeds of 40 MB/s.
Why are encrypted writes so much slower than encrypted reads?
(And no, I'm not doing something silly like benchmarking in a VM. I swear I've already thought of all the "easy" answers and they don't explain the situation as far as I can tell.)
user541686
Posted 2018-04-28T05:51:12.567
Reputation: 21 330
Possible duplicate of Is a VeraCrypt partition slower?
– Keltari – 2018-04-28T06:16:43.3631"Why are encrypted writes so much slower than encrypted reads?" The unencrypted write time should be significantly longer than the read time, so that benchmark is suspect. But the encryption process takes longer than the decryption process. It isn't clear what level of detail you're looking for to explain the difference. – fixer1234 – 2018-04-28T06:52:07.507
@fixer1234: "The unencrypted write time should be significantly longer than the read time, so that benchmark is suspect." ...no, my benchmark isn't suspect; you just haven't seen fast SSDs. However, I'm not aware of encryption taking 20x more time than decryption; it should be about the same as far as I'm aware. If you believe otherwise, you don't really need any detail to prove it: just show me a program (or use standard OpenSSL commands) that demonstrate encryption taking 20x longer than decryption. I'll happily accept such an answer. – user541686 – 2018-04-28T07:32:05.140
@Keltari: No, this isn't a duplicate of that... my read speed is so ridiculously faster than my write speed, even for the encrypted partition. That guy was just wondering why encryption was slower than plaintext... it doesn't explain the read-write discrepancy. – user541686 – 2018-04-28T07:35:10.263
What model CPU do you have? – davidgo – 2018-04-28T09:13:15.823
@davidgo: I don't see how the model could possibly explain the read vs. write difference, but 7820HQ... – user541686 – 2018-04-28T10:06:17.883
It won't be the issue in your build - but I was wondering if the CPU was lacking AeS-NI support. – davidgo – 2018-04-28T19:09:11.153
@davidgo: Yeah I got that part, but how would that make the read so much faster than the write? – user541686 – 2018-04-28T19:11:22.447