Hi there,
Somewhat related to my question about TRIM, I recently thought my SSDs
were performing badly (for NVMe drives) when transferring files between
them - it seems to be very SATA-ish speeds of around 500-600MB/s when
transferring files between drives (one for my home partition, the other
for the ridiculous number of VMs I need).
It turns out this was not due to TRIM, but due to eCryptFS:
When dd'ing with an 8 MB block size, both disks can write at about
1.6GB/s - as expected.
When dd'ing to the eCryptFS part of my /home partition, I get write
speeds of about 600MB/s and read speeds of 1.2GB/s. I get speeds of
800MB/s when transferring from the eCrpytFS'd part of /home to my VMs
drive, but if 1.8GB/s from the unencrypted portion.
TL;DR: on my CPU (Ryzen 3600 at stock clock speeds) the eCryptFS
encryption speeds just so happen to limit drives to SATA-ish speeds for
both transfers in and out of the encrypted area. I suspect the transfer
out of the eCryptFS storage being slower than just dumping to /dev/null
is due to the IO being very single-threaded in the kernel?
At any rate, the encryption/decryption is definitely single-threaded.
Thank you for coming to my TED talk that you neither volunteered to
attend, and (probably) nor were especially interested to read :)
Hamish
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