Re: [gentoo-user] Getting maximum space out of a hard drive

[Rich Freeman <rich0@gentoo.org>]

On Sat, Aug 20, 2022 at 3:15 PM Dale <rdalek1967@gmail.com> wrote:
>
> Related question.  Does encryption slow the read/write speeds of a drive
> down a fair amount?  This new 10TB drive is maxing out at about
> 49.51MB/s or so.

Encryption won't impact the write speeds themselves of course, but it
could introduce a CPU bottleneck.  If you don't have any cores pegged
at 100% though I'd say this isn't happening.  On x86 encrypting a hard
drive shouldn't be a problem. I have seen it become a bottleneck on
something like a Pi4 if the encryption isn't directly supported in
hardware by the CPU.

50MB/s is reasonable if you have an IOPS-limited workload.  It is of
course a bit low for something that is bandwidth-limited.  If you want
to test that I'm not sure rsync is a great way to go.  I'd pause that
(ctrl-z is fine), then verify that all disk IO goes to zero (might
take 30s to clear out the cache).  Then I'd use "time dd bs=1M
count=20000 if=/dev/zero of=/path/to/drive/test"  to measure how long
it takes to create a 20GB file.  Oh, this assumes you're not using a
filesystem that can detect all-zeros and compress or make the file
sparse.  If you get crazy-fast results then I'd do a test like copying
a single large file with cp and timing that.

Make sure your disk has no IO before testing.  If you have two
processes accessing at once then you're going to get a huge drop in
performance on a spinning disk.  That includes one writing process and
one reading one, unless the reads all hit the cache.

-- 
Rich